U.S. patent number 8,157,874 [Application Number 13/087,117] was granted by the patent office on 2012-04-17 for engineered fuel feed stock.
This patent grant is currently assigned to Re Community Holdings II, Inc.. Invention is credited to Dingrong Bai, James W. Bohlig.
United States Patent |
8,157,874 |
Bohlig , et al. |
April 17, 2012 |
**Please see images for:
( Certificate of Correction ) ** |
Engineered fuel feed stock
Abstract
Disclosed are novel engineered fuel feed stocks, feed stocks
produced by the described processes, and methods of making the fuel
feed stocks. Components derived from processed MSW waste streams
can be used to make such feed stocks which are substantially free
of glass, metals, grit and noncombustibles. These feed stocks are
useful for a variety of purposes including as gasification and
combustion fuels.
Inventors: |
Bohlig; James W. (Rutland Town,
VT), Bai; Dingrong (Rutland, VT) |
Assignee: |
Re Community Holdings II, Inc.
(Rutland, VT)
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Family
ID: |
41444961 |
Appl.
No.: |
13/087,117 |
Filed: |
April 14, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110209398 A1 |
Sep 1, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12492096 |
Jun 25, 2009 |
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61076020 |
Jun 26, 2008 |
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61076025 |
Jun 26, 2008 |
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Current U.S.
Class: |
44/589; 44/552;
241/17 |
Current CPC
Class: |
C10J
3/72 (20130101); C10L 5/40 (20130101); C10J
3/463 (20130101); C01B 3/02 (20130101); C10L
5/403 (20130101); C10L 5/36 (20130101); C10L
5/366 (20130101); C10L 5/406 (20130101); C10L
5/08 (20130101); C10L 5/363 (20130101); C10L
5/46 (20130101); C10L 5/445 (20130101); C10L
2290/30 (20130101); Y02P 20/145 (20151101); C10J
2300/0909 (20130101); C10J 2300/0946 (20130101); C10J
2300/0903 (20130101); C10L 2290/24 (20130101); Y02E
20/18 (20130101); C10J 2300/0916 (20130101); C10L
2200/0469 (20130101); C10J 2300/0906 (20130101); C10L
2250/04 (20130101); Y02E 50/10 (20130101); Y02E
50/30 (20130101); C10J 2300/092 (20130101); C10L
2290/28 (20130101) |
Current International
Class: |
C10L
5/46 (20060101); B03B 5/48 (20060101) |
Field of
Search: |
;44/504,505,550,552,567,589,593-596,606,629,605,628,903,590
;48/197FM ;241/17 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101215490 |
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Jul 2008 |
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CN |
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2005-290129 |
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Oct 2005 |
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JP |
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WO 2005/097684 |
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Oct 2005 |
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WO |
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WO 2007/123510 |
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Nov 2007 |
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WO |
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WO 2007/147244 |
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Dec 2007 |
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WO |
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Other References
"paper," "waste, domestic organic waste from the municipal
collection," "douglas fir," and "wood, sawdust," 12 pages, from
BIOBIB a Data Base for Biofuels
(www.vt.tuwien.ac.at/biobib/biobib.html information available
online 2007 and earlier). cited by other .
Arena et al., "Gasification of a Plastic Waste in a Pilot Fluidized
Bed Reactor," 7 pages, 10th Conference on Process Integration,
Modelling and Optimisation for Energy Saving and Pollution
Reduction, Ischia Island, Gulf of Naples, Jun. 24-27, 2007. cited
by other .
Aznar et al., "Plastic waste elimination by co-gasification with
coal and biomass in fluidized bed with air in pilot plant," Fuel
Processing Technology 87(5):409-420 (2006). cited by other .
Blasi, "Influence of physical properties on biomass
devolitilization characteristics," Fuel 76(10):957-964 (1997).
cited by other .
International Search Report issued for PCT/US09/48718, mailed on
Aug. 13, 2009 (2 pages). cited by other .
International Search Report issued for PCT/US09/48719, mailed on
Sep. 16, 2009 (2 pages). cited by other .
International Search Report issued for PCT/US10/57351, mailed on
Feb. 2, 2011 (3 pages). cited by other .
International Search Report issued for PCT/US10/61228, mailed on
Feb. 22, 2011 (3 pages). cited by other .
Prins et al., "From coal to biomass gasification: Comparison of
thermodynamic efficiency," Energy 32:1248-1259 (2007). cited by
other .
Written Opinion of the International Searching Authority issued for
PCT/US09/48719, mailed on Sep. 16, 2009 (7 pages). cited by other
.
Written Opinion of the International Searching Authority issued for
PCT/US09/48718, mailed on Aug. 13, 2009 (7 pages). cited by other
.
Written Opinion of the International Searching Authority issued for
PCT/US10/61228, mailed on Feb. 22, 2011 (11 pages). cited by other
.
Written Opinion of the International Searching Authority issued for
PCT/US10/57351, mailed on Feb. 2, 2011 (14 pages). cited by
other.
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Primary Examiner: Toomer; Cephia D
Assistant Examiner: Weiss; Pamela H
Attorney, Agent or Firm: Cooley LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. application Ser. No.
12/492,096 filed Jun. 25, 2009, which claims priority to U.S.
Application Ser. No. 61/076,025, filed on Jun. 26, 2008, and U.S.
Application Ser. No. 61/076,020, filed Jun. 26, 2008, the
disclosures of which are hereby incorporated by reference in their
entireties for all purposes.
Claims
The invention claimed is:
1. A method of producing an engineered fuel feed stock from a
processed MSW waste stream, the method comprising the steps of: a)
selecting a plurality components from a processed MSW waste stream
which components in combination have chemical molecular
characteristics comprising a carbon content of between about 40 wt
% and about 50 wt %, a hydrogen content of between about 4 wt % and
about 9 wt %, an ash content of less than 5 wt %, an O/C ratio of
between about 0.8 and about 1.0; an H/C ratio of between about 0.1
and about 0.14; and wherein the engineered fuel feed stock contains
biodegradable waste and non-biodegradable waste and substantially
no glass, metals, grit, and noncombustibles; b) combining the
selected components of step a) to form an engineered fuel feed
stock; c) comparing the resulting chemical molecular
characteristics of the engineered fuel feed stock of step b) with
the chemical molecular characteristics of step a); d) optionally
adding other fuel components to the engineered fuel feed stock of
step b) if the chemical molecular characteristics of the feed stock
of step b) do not fall within the chemical molecular
characteristics of step a).
2. The method of claim 1, wherein the engineered fuel feed stock
has a moisture content of between about 1 wt % and about 10 wt
%.
3. The method of claim 1, wherein the engineered fuel feed stock
has a sulfur content of less than about 0.5 wt %.
4. The method of claim 1, wherein the engineered fuel feed stock
has a chlorine content of less than about 1 wt %.
5. The method of claim 1, wherein the engineered fuel feed stock
has a HHV of between about 7,000 BTU/lb and about 11,000
BTU/lb.
6. The method of claim 1, wherein the engineered fuel feed stock
has a volatile matter content of about 60 wt % to about 70 wt
%.
7. The method of claim 1, wherein the engineered fuel feed stock is
comminuted.
8. The method of claim 1, wherein the engineered fuel feed stock is
densified.
9. The method of claim 1, wherein the densified engineered fuel
feed stock is in the form of a pellet.
10. A method of producing an engineered fuel feed stock, the method
comprising: a) receiving a plurality of MSW waste streams; b)
selecting the engineered fuel feed stock to have chemical molecular
characteristics comprising: a carbon content of between about 40 wt
% and about 50 wt %, a hydrogen content of between about 4 wt % and
about 9 wt %, an ash content of less than 5 wt %, an O/C ratio of
between about 0.8 and about 1.0; and an H/C ratio of between about
0.1 and about 0.14, and wherein the engineered fuel feed stock
contains biodegradable waste and non-biodegradable waste and
substantially no glass, metals, grit, and noncombustibles; c)
inventorying the components of the plurality of MSW waste streams
based on the chemical molecular characteristics of the components;
d) comparing the chemical molecular characteristics of the
inventoried components of the plurality of MSW waste streams of
step c) with the selected chemical molecular characteristics of
step b); and e) optionally adding additional fuel components with
the required chemical molecular characteristics to the inventoried
components of step c) to meet the desired chemical molecular
characteristics of step b) for the engineered fuel feed stock.
11. The method of claim 10, wherein the engineered fuel feed stock
has a moisture content of between about 1 wt % and about 10 wt
%.
12. The method of claim 10, wherein the engineered fuel feed stock
has a sulfur content of less than about 0.5 wt %.
13. The method of claim 10, wherein the engineered fuel feed stock
has a chlorine content of less than about 1 wt %.
14. The method of claim 10, wherein the engineered fuel feed stock
has a HHV of between about 7,000 BTU/lb and about 11,000
BTU/lb.
15. The method of claim 10, wherein the engineered fuel feed stock
has a volatile matter content of about 60 wt % to about 70 wt
%.
16. The method of claim 10, wherein the engineered fuel engineered
fuel feed stock is comminuted.
17. The method of claim 10, wherein the engineered fuel engineered
fuel feed stock is densified in the form of a pellet.
Description
FIELD OF THE INVENTION
The present invention relates to alternative fuels. In particular,
the invention relates to engineering engineered fuel feed stock
suited for specific applications including as a fossil fuel
substitute for combustion, as well as feed stock for gasification
to produce high quality synthesis gas. Feed stock can be engineered
to control air emission profiles upon combustion or gasification
(such as dioxins, sulfur emitted, as well as others pollutants) as
well as to avoid slagging. The feed stock described herein
comprises at least one component of processed municipal solid
waste, and optionally other components.
BACKGROUND OF THE INVENTION
Sources of fossil fuels useful for heating, transportation, and the
production of chemicals as well as petrochemicals are becoming
increasingly more scarce and costly. Industries such as those
producing energy and petrochemicals are actively searching for cost
effective engineered fuel feed stock alternatives for use in
generating those products and many others. Additionally, due to the
ever increasing costs of fossil fuels, transportation costs for
moving engineered fuel feed stocks for production of energy and
petrochemicals is rapidly escalating.
These energy and petrochemical producing industries, and others,
have relied on the use of fossil fuels, such as coal and oil and
natural gas, for use in combustion and gasification processes for
the production of energy, for heating and electricity, and the
generation of synthesis gas used for the downstream production of
chemicals and liquid fuels, as well as an energy source for
turbines.
Combustion and gasification are thermochemical processes that are
used to release the energy stored within the fuel source.
Combustion takes place in a reactor in the presence of excess air,
or excess oxygen. Combustion is generally used for generating steam
which is used to power turbines for producing electricity. However,
the brute force nature of the combustion of fuel causes significant
amounts of pollutants to be generated in the gas produced. For
example, combustion in an oxidizing atmosphere of, for example,
fossil fuels such as coal, oil and natural gas, releases nitrogen
oxides, a precursor to ground level ozone which can stimulate
asthma attacks. Combustion is also the largest source of sulfur
dioxide which in turn produces sulfates that are very fine
particulates. Fine particle pollution from U.S. power plants cuts
short the lives of over 30,000 people each year. Hundreds of
thousands of Americans suffer from asthma attacks, cardiac problems
and upper and lower respiratory problems associated with fine
particles from power plants.
Gasification also takes place in a reactor, although in the absence
of air, or in the presence of substoichiometric amounts of oxygen.
The thermochemical reactions that take place in the absence of
oxygen or under substoichiometric amounts of oxygen do not result
in the formation of nitrogen oxides or sulfur oxides. Therefore,
gasification can eliminate much of the pollutants formed during the
firing of fuel.
Gasification generates a gaseous, fuel rich product known as
synthesis gas (syngas). During gasification, two processes take
place that convert the fuel source into a useable fuel gas. In the
first stage, pyrolysis releases the volatile components of the fuel
at temperatures below 600.degree. C. (1112.degree. F.), a process
known as devolatization. The pyrolysis also produces char that
consists mainly of carbon or charcoal and ash. In the second
gasification stage, the carbon remaining after pyrolysis is either
reacted with steam, hydrogen, or pure oxygen. Gasification with
pure oxygen results in a high quality mixture of carbon monoxide
and hydrogen due to no dilution of nitrogen from air.
A variety of gasifier types have been developed. They can be
grouped into four major classifications: fixed-bed updraft,
fixed-bed downdraft, bubbling fluidized-bed and circulating
fluidized bed. Differentiation is based on the means of supporting
the fuel source in the reactor vessel, the direction of flow of
both the fuel and oxidant, and the way heat is supplied to the
reactor. The advantages and disadvantages of these gasifier designs
have been well documented in literature, for example, Rezaiyan, J.
and Nicholas P. Cheremisinoff, Gasification Technology A Primer for
Engineers and Scientists. Boca Raton: CRC Press, 2005, the contents
of which are hereby incorporated by reference.
The updraft gasifier, also known as counterflow gasification, is
the oldest and simplest form of gasifier; it is still used for coal
gasification. The fuel is introduced at the top of the reactor, and
a grate at the bottom of the reactor supports the reacting bed. The
oxidant in the form of air or oxygen and/or steam are introduced
below the grate and flow up through the bed of fuel and char.
Complete combustion of char takes place at the bottom of the bed,
liberating CO.sub.2 and H.sub.2O. These hot gases
(.about.1000.degree. C.) pass through the bed above, where they are
reduced to H.sub.2 and CO and cooled to about 750.degree. C.
Continuing up the reactor, the reducing gases (H.sub.2 and CO)
pyrolyse the descending dry fuel and finally dry any incoming wet
fuel, leaving the reactor at a low temperature (.about.500.degree.
C.). Updraft gasification is a simple, low cost process that is
able to handle fuel with a high moisture and high inorganic
content. The primary disadvantage of updraft gasification is that
the synthesis gas contains 10-20% tar by weight, requiring
extensive syngas cleanup before engine, turbine or synthesis
applications.
Downdraft gasification, also known as concurrent-flow gasification,
has the same mechanical configuration as the updraft gasifier
except that the oxidant and product gases flow down the reactor, in
the same direction as the fuel, and can combust up to 99.9% of the
tars formed. Low moisture fuel (<20%) and air or oxygen are
ignited in the reaction zone at the top of the reactor, generating
pyrolysis gas/vapor, which burns intensely leaving 5 to 15% char
and hot combustion gas. These gases flow downward and react with
the char at 800 to 1200.degree. C., generating more CO and H.sub.2
while being cooled to below 800.degree. C. Finally, unconverted
char and ash pass through the bottom of the grate and are sent to
disposal. The advantages of downdraft gasification are that up to
99.9% of the tar formed is consumed, requiring minimal or no tar
cleanup. Minerals remain with the char/ash, reducing the need for a
cyclone. The disadvantages of downdraft gasification are that it
requires feed drying to a low moisture content (<20%). The
syngas exiting the reactor is at high temperature, requiring a
secondary heat recovery system; and 4-7% of the carbon remains
unconverted.
The bubbling fluidized bed consists of fine, inert particles of
sand or alumina, which have been selected for size, density, and
thermal characteristics. As gas (oxygen, air or steam) is forced
through the inert particles, a point is reached when the frictional
force between the particles and the gas counterbalances the weight
of the solids. At this gas velocity (minimum fluidization), the
solid particles become suspended, and bubbling and channeling of
gas through the media may occur, such that the particles remain in
the reactor and appear to be in a "boiling state". The minimum
fluidization velocity is not equal to the minimum bubbling velocity
and channeling velocity. For coarse particles, the minimum bubbling
velocity and channeling velocity are close or almost equal, but the
channeling velocity may be quite different, due to the gas
distribution problem. The fluidized particles tend to break up the
fuel fed to the bed and ensure good heat transfer throughout the
reactor. The advantages of bubbling fluidized-bed gasification are
that it yields a uniform product gas and exhibits a nearly uniform
temperature distribution throughout the reactor. It is also able to
accept a wide range of fuel particle sizes, including fines;
provides high rates of heat transfer between inert material, fuel
and gas.
The circulating fluidized bed gasifiers operate at gas velocities
higher than the so-called transport velocity or onset velocity of
circulating fluidization at which the entertainment of the bed
particles dramatically increases so that continuous feeding or
recycling back the entrained particles to the bed is required to
maintain a stable gas-solid system in the bed. --The circulating
fluidized-bed gasification is suitable for rapid reactions offering
high heat transport rates due to high heat capacity of the bed
material. High conversion rates are possible with low tar and
unconverted carbon.
Normally these gasifiers use a homogeneous source of fuel. A
constant unchanging fuel source allows the gasifier to be
calibrated to consistently form the desired product. Each type of
gasifier will operate satisfactorily with respect to stability, gas
quality, efficiency and pressure losses only within certain ranges
of the fuel properties. Some of the properties of fuel to consider
are energy content, moisture content, volatile matter, ash content
and ash chemical composition, reactivity, size and size
distribution, bulk density, and charring properties. Before
choosing a gasifier for any individual fuel it is important to
ensure that the fuel meets the requirements of the gasifier or that
it can be treated to meet these requirements. Practical tests are
needed if the fuel has not previously been successfully
gasified.
Normally, gasifiers use a homogeneous source of fuel for producing
synthesis gas. A constant unchanging fuel source allows the
gasifier to be calibrated to consistently form the desired product.
Each type of gasifier will operate satisfactorily with respect to
stability, gas quality, efficiency and pressure losses only within
certain ranges of the fuel properties. Some of the properties of
fuel to consider for combustion and gasification are high heating
value (HHV) content, carbon (C), hydrogen (H), and oxygen (O)
content, BTU value, moisture content, volatile matter content, ash
content and ash chemical composition, sulfur content, chlorine
content, reactivity, size and size distribution, and bulk density.
Before choosing a gasifier for any individual fuel it is important
to ensure that the fuel meets the requirements of the gasifier or
that it can be treated to meet these requirements. Practical tests
are needed if the fuel has not previously been successfully
gasified.
One potential source for a large amount of feed stock for
gasification is waste. Waste, such as municipal solid waste (MSW),
is typically disposed of or used in combustion processes to
generate heat and/or steam for use in turbines. The drawbacks
accompanying combustion have been described above, and include the
production of pollutants such as nitrogen oxides, sulfur oxide,
particulates and products of chlorine that damage the
environment.
One of the most significant threats facing the environment today is
the release of pollutants and greenhouse gases (GHGs) into the
atmosphere through the combustion of fuels. GHGs such as carbon
dioxide, methane, nitrous oxide, water vapor, carbon monoxide,
nitrogen oxide, nitrogen dioxide, and ozone, absorb heat from
incoming solar radiation but do not allow long-wave radiation to
reflect back into space. GHGs in the atmosphere result in the
trapping of absorbed heat and warming of the earth's surface. In
the U.S., GHG emissions come mostly from energy use driven largely
by economic growth, fuel used for electricity generation, and
weather patterns affecting heating and cooling needs.
Energy-related carbon dioxide emissions, resulting from petroleum
and natural gas, represent 82 percent of total U.S. human-made GHG
emissions. Another greenhouse gas, methane, comes from landfills,
coal mines, oil and gas operations, and agriculture; it represents
nine percent of total emissions. Nitrous oxide (5 percent of total
emissions), meanwhile, is emitted from burning fossil fuels and
through the use of certain fertilizers and industrial processes.
World carbon dioxide emissions are expected to increase by 1.9
percent annually between 2001 and 2025. Much of the increase in
these emissions is expected to occur in the developing world where
emerging economies, such as China and India, fuel economic
development with fossil energy. Developing countries' emissions are
expected to grow above the world average at 2.7 percent annually
between 2001 and 2025; and surpass emissions of industrialized
countries near 2018.
Waste landfills are also significant sources of GHG emissions,
mostly because of methane released during decomposition of waste,
such as, for example, MSW. Compared with carbon dioxide, methane is
twenty-times stronger than carbon dioxide as a GHG, and landfills
are responsible for about 4% of the anthropogenic emissions.
Considerable reductions in methane emissions can be achieved by
combustion of waste and by collecting methane from landfills. The
methane collected from the landfill can either be used directly in
energy production or flared off, i.e., eliminated through
combustion without energy production (Combustion Of Waste May
Reduce Greenhouse Gas Emissions, ScienceDaily, Dec. 8, 2007).
One measure of the impact human activities have on the environment
in terms of the amount of green house gases produced is the carbon
footprint, measured in units of carbon dioxide (CO.sub.2). The
carbon footprint can be seen as the total amount of carbon dioxide
and other GHGs emitted over the full life cycle of a product or
service. Normally, a carbon footprint is usually expressed as a
CO.sub.2 equivalent (usually in kilograms or tons), which accounts
for the same global warming effects of different GHGs. Carbon
footprints can be calculated using a Life Cycle Assessment method,
or can be restricted to the immediately attributable emissions from
energy use of fossil fuels.
An alternative definition of carbon footprint is the total amount
of CO.sub.2 attributable to the actions of an individual (mainly
through their energy use) over a period of one year. This
definition underlies the personal carbon calculators. The term owes
its origins to the idea that a footprint is what has been left
behind as a result of the individual's activities. Carbon
footprints can either consider only direct emissions (typically
from energy used in the home and in transport, including travel by
cars, airplanes, rail and other public transport), or can also
include indirect emissions which include CO.sub.2 emissions as a
result of goods and services consumed, along with the concomitant
waste produced.
The carbon footprint can be efficiently and effectively reduced by
applying the following steps: (i) life cycle assessment to
accurately determine the current carbon footprint; (ii)
identification of hot-spots in terms of energy consumption and
associated CO.sub.2-emissions; (iii) optimization of energy
efficiency and, thus, reduction of CO.sub.2-emissions and reduction
of other GHG emissions contributed from production processes; and
(iv) identification of solutions to neutralize the CO.sub.2
emissions that cannot be eliminated by energy saving measures. The
last step includes carbon offsetting, and investment in projects
that aim at the reducing CO.sub.2 emissions.
The purchase of carbon offsets is another way to reduce a carbon
footprint. One carbon offset represents the reduction of one ton of
CO.sub.2-eq. Companies that sell carbon offsets invest in projects
such as renewable energy research, agricultural and landfill gas
capture, and tree-planting.
Purchase and withdrawal of emissions trading credits also occur,
which creates a connection between the voluntary and regulated
carbon markets. Emissions trading schemes provide a financial
incentive for organizations and corporations to reduce their carbon
footprint. Such schemes exist under cap-and-trade systems, where
the total carbon emissions for a particular country, region, or
sector are capped at a certain value, and organizations are issued
permits to emit a fraction of the total emissions. Organizations
that emit less carbon than their emission target can then sell
their "excess" carbon emissions.
For many wastes, the disposed materials represent what is left over
after a long series of steps including: (i) extraction and
processing of raw materials; (ii) manufacture of products; (iii)
transportation of materials and products to markets; (iv) use by
consumers; and (v) waste management. At virtually every step along
this "life cycle," the potential exists for greenhouse gas (GHG)
impacts. Waste management affects GHGs by affecting energy
consumption (specifically, combustion of fossil fuels) associated
with making, transporting, using, and disposing the product or
material that becomes a waste and emissions from the waste in
landfills where the waste is disposed.
Incineration typically reduces the volume of the MSW by about 90%
with the remaining 10% of the volume of the original MSW still
needing to be landfilled. This incineration process produces large
quantities of the GHG CO.sub.2. Typically, the amount of energy
produced per equivalents CO.sub.2 expelled during incineration are
very low, thus making incineration of MSW for energy production one
of the worst offenders in producing GHG released into the
atmosphere. Therefore, if GHGs are to be avoided, new solutions for
the disposal of wastes, such as MSW, other than landfilling and
incineration, are needed.
Each material disposed of as waste has a different GHG impact
depending on how it is made and disposed. The most important GHGs
for waste management options are carbon dioxide, methane, nitrous
oxide, and perfluorocarbons. Of these, carbon dioxide (CO.sub.2) is
by far the most common GHG emitted in the US. Most carbon dioxide
emissions result from energy use, particularly fossil fuel
combustion. Carbon dioxide is the reference gas for measurement of
the heat-trapping potential (also known as global warming potential
or GWP). By definition, the GWP of one kilogram (kg) of carbon
dioxide is 1. Methane has a GWP of 21, meaning that one kg of
methane has the same heat-trapping potential as 21 kg of CO.sub.2.
Nitrous oxide has a GWP of 310. Perfluorocarbons are the most
potent GHGs with GWPs of 6,500 for CF.sub.4 and 9,200 for
C.sub.2F.sub.6. Emissions of carbon dioxide, methane, nitrous
oxide, and perfluorocarbons are usually expressed in "carbon
equivalents." Because CO.sub.2 is 12/44 carbon by weight, one
metric ton of CO.sub.2 is equal to 12/44 or 0.27 metric tons of
carbon equivalent (MTCE). The MTCE value for one metric ton of each
of the other gases is determined by multiplying its GWP by a factor
of 12/44 (The Intergovernmental Panel on Climate Change (IPCC),
Climate Change 1995: The Science of Climate Change, 1996, p. 121).
Methane (CH.sub.4), a more potent GHG, is produced when organic
waste decomposes in an oxygen free (anaerobic) environment, such as
a landfill. Methane from landfills is the largest source of methane
in the US.
The greater GHG emission reductions are usually obtained when
recycled waste materials are processed and used to replace fossil
fuels. If the replaced material is biogenic (material derived from
living organisms), it is not always possible to obtain reductions
of emissions. Even other factors, such as the treatment of the
waste material and the fate of the products after the use, affect
the emissions balance. For example, the recycling of oil-absorbing
sheets made of recycled textiles lead to emission reductions
compared with the use of virgin plastic. In another example, the
use of recycled plastic as raw material for construction material
was found to be better than the use of impregnated wood. This is
because the combustion of plastic causes more emissions than
impregnated wood for reducing emissions. If the replaced material
had been fossil fuel-based, or concrete, or steel, the result would
probably have been more favorable to the recycling of plastic.
Given the effect of GHGs on the environment, different levels of
government are considering, and in some instances have initiated,
programs aimed at reducing the GHGs released into the atmosphere
during the conversion of fuels into energy. One such initiative is
the Regional Greenhouse Gas Initiative (RGGI). RGGI is a
market-based program designed to reduce global warming pollution
from electric power plants in the Northeast. Other such initiatives
are being considered in different sections of the U.S. and on the
federal level. RGGI is a government mandated GHG trading system in
the Northeastern U.S. This program will require, for example, that
coal-fired power plants aggressively reduce their GHG emissions by
on average 2.5% per year. One way to do this is by changing the
fuel source used or scrubbing the emissions to remove the
pollutants. An alternative is to purchase carbon credits generated
by others which can offset their emissions into the atmosphere.
Other emissions to be avoided are sulfur emissions as well as
chlorine emissions. Fuels and waste containing significant amounts
of sulfur or chlorine should be avoided for combustion and
gasification reactions. Significant amounts are defined as an
amount that when added to a final fuel feed stock causes the final
feed stock to have more than 2% sulfur or more than 1% of chlorine.
Materials such as coal, used tires, carpet, and rubber, when
combusted, release unacceptable amounts of harmful sulfur- and
chlorine-based gases.
Thus, there is a need for alternative fuels that burn efficiently
and cleanly and that can be used for the production of energy
and/or chemicals. There is at the same time a need for waste
management systems that implement methods for reducing GHG
emissions of waste by utilizing such wastes. In particular, there
is a need for reducing the carbon foot print of materials by
affecting their end-stage life cycle management. By harnessing and
using the energy content contained in waste, it is possible to
reduce GHG emissions generated during the processing of wastes and
effectively use the waste generated by commercial and residential
consumers.
It is an object of the present invention to provide an engineered
fuel feed stock (EF) containing specified chemical molecular
characteristics, such as carbon content, hydrogen content, oxygen
content, sulfur content, ash content, moisture content, and HHV for
thermal-conversion of carbon-containing materials. The engineered
fuel feed stock is useful for many purposes including, but not
limited to, production of synthesis gas. Synthesis gas, in turn, is
useful for a variety of purposes including for production of liquid
fuels by Fischer-Tropsch technology.
SUMMARY OF THE INVENTION
The present disclosure describes an engineered fuel feed stock
comprising at least one component derived from a processed MSW
waste stream, the feed stock possessing a range of chemical
molecular characteristics which make it useful for a variety of
combustion and gasification purposes. Purposes such as generating
energy when used as a substitute for coal or as a supplement to
coal is described, as well as a source feed stock for use in
gasification and production of synthesis gas. The feed stock can be
in the form of loose material, densified cubes, briquettes,
pellets, or other suitable shapes and forms. A process of producing
engineered fuel feed stock is described which comprises the process
in which a plurality of waste streams, including solid and liquid
wastes, are processed and, where necessary, separated in a
materials recovery center so as to inventory the components which
comprise the waste streams. In some embodiments, the materials
comprising the waste stream in the materials recovery facility are
inventoried for chemical molecular characteristics, without
separation, and this inventoried material can be stored for
subsequent use when producing a desired engineered fuel feed stock
having a particular chemical molecular profile. In other
embodiments, the materials comprising the waste stream entering the
materials recovery facility are separated according to their
chemical molecular characteristics and inventoried separately for
use in producing an engineered fuel feed stock. These materials
comprising the waste stream entering the materials recovery
facility, when undergoing separation, can be positively or
negatively selected for, based on, for example, BTU fuel content,
carbon content, hydrogen content, ash content, chlorine content, or
any other suitable characteristics, for gasification or combustion.
Methods for making the engineered fuel feed stock described herein
are also described.
Algorithms for engineering HHV fuels are disclosed. HHV fuels can
be designed, for example, to have the highest possible heat content
with a tolerable ash content in order to prevent slagging. These
fuels have comparable energy density (BTU/lb) to coal, but without
the problems of slagging, fusion and sulfur pollution, and can
serve as a substitute for coal or a supplement to coal. Also,
engineered fuel feed stocks can be designed, for example, to
produce high quality syngas by optimizing the content of C, H, and
O in the feed stock prior to gasification. Such engineered fuel
feed stocks produce high quality syngas in terms of HHV if the
syngas is to be used for power generation applications or
H.sub.2/CO ratios, amounts of CO and H.sub.2 present in the product
syngas in the event that the syngas is to be used in chemical
synthetic applications. Also, engineered fuel feed stocks can be
engineered so as to minimize harmful emissions, for example,
engineered feed stocks comprising less than 2% sulfur content.
Various waste stream components, including recyclable materials and
recycling residue, can be used to produce the desired engineered
fuel feed stock. Although at any given time during the life cycle
of the waste entering the materials recovery facility, it may be
determined that the highest and best use for some or all of the
components of the waste streams is for them to be recycled.
Accordingly, in one aspect the present invention provides an
engineered fuel feed stock, comprising a component derived from a
processed MSW waste stream, the feed stock having a carbon content
of between about 30% and about 80%, a hydrogen content of between
about 3% and about 10%, an ash content of less than about 10%, a
sulfur content of less than 2%, and a chlorine content of less than
about 1%. In some embodiments, the feed stock has a HHV of between
about 3,000 BTU/lb and about 15,000 BTU/lb. In some embodiments,
the feed stock has a volatile matter content of about 40% to about
80%. In some embodiments, the feed stock has a moisture content of
less than about 30%. In some embodiments, the feed stock has a
moisture content of between about 10% and about 30%. In other
embodiments, the feed stock has a moisture content of between about
10% and about 20%. In still further embodiments, the feed stock has
a moisture content of about 1% and about 10%. The engineered fuel
feed stock contains substantially no glass, metal, grit and
noncombustibles (other than those necessary to cause the engineered
fuel feed stock to be inert).
In some embodiments, the feed stock has a carbon content of between
about 40% and about 70%. In some embodiments, the feed stock has a
carbon content of between about 50% and about 60%. In some
embodiments, the feed stock has a carbon content of between about
30% and about 40%. In some embodiments, the feed stock has a carbon
content of between about 40% and about 50%. In some embodiments,
the feed stock has a carbon content of between about 60% and about
70%. In some embodiments, the feed stock has a carbon content of
between about 70% and about 80%. In some embodiments, the feed
stock has a carbon content of about 35%. In some embodiments, the
feed stock has a carbon content of about 45%. In some embodiments,
the feed stock has a carbon content of about 55%. In some
embodiments, the feed stock has a carbon content of about 65%. In
some embodiments, the feed stock has a carbon content of about
75%.
In some embodiments, the feed stock has a hydrogen content of
between about 4% and about 9%. In some embodiments, the feed stock
has a hydrogen content of between about 5% and about 8%. In some
embodiments, the feed stock has a hydrogen content of between about
6% and about 7%.
In some embodiments, the feed stock has a moisture content of
between about 12% and about 28%. In some embodiments, the feed
stock has a moisture content of between about 14% and about 24%. In
some embodiments, the feed stock has a moisture content of between
about 16% and about 22%. In some embodiments, the feed stock has a
moisture content of between about 18% and about 20%.
In some embodiments, the feed stock has an ash content of less than
about 10%. In some embodiments, the feed stock has an ash content
of less than about 9%. In some embodiments, the feed stock has an
ash content of less than about 8%. In some embodiments, the feed
stock has an ash content of less than about 7%. In some
embodiments, the feed stock has an ash content of less than about
6%. In some embodiments, the feed stock has an ash content of less
than about 5%. In some embodiments, the feed stock has an ash
content of less than about 4%. In some embodiments, the feed stock
has an ash content of less than about 3%.
In some embodiments, the feed stock has a HHV of between about
3,000 BTU/lb and about 15,000 BTU/lb. In some embodiments, the feed
stock has a HHV of between about 4,000 BTU/lb and about 14,000
BTU/lb. In some embodiments, the feed stock has a HHV of between
about 5,000 BTU/lb and about 13,000 BTU/lb. In some embodiments,
the feed stock has a HHV of between about 6,000 BTU/lb and about
12,000 BTU/lb. In some embodiments, the feed stock has a HHV of
between about 7,000 BTU/lb and about 11,000 BTU/lb. In some
embodiments, the feed stock has a HHV of between about 8,000 BTU/lb
and about 10,000 BTU/lb. In some embodiments, the feed stock has a
HHV of about 9,000 BTU/lb.
In some embodiments, the feed stock has a volatile matter content
of about 50% to about 70%. In some embodiments, the feed stock has
a volatile matter content of about 60%.
In some embodiments, the engineered fuel feed stock has a ratio of
H/C from about 0.025 to about 0.20. In some embodiments, the
engineered fuel feed stock has a ratio of H/C from about 0.05 to
about 0.18. In some embodiments, the engineered fuel feed stock has
a ratio of H/C from about 0.07 to about 0.16. In some embodiments,
the engineered fuel feed stock has a ratio of H/C from about 0.09
to about 0.14. In some embodiments, the engineered fuel feed stock
has a ratio of H/C from about 0.10 to about 0.13. In some
embodiments, the engineered fuel feed stock has a ratio of H/C from
about 0.11 to about 0.12. In some embodiments, the engineered fuel
feed stock has a ratio of H/C of about 0.13. In some embodiments,
the engineered fuel feed stock has a ratio of H/C of about
0.08.
In some embodiments, the engineered fuel feed stock has an O/C
ratio from about 0.01 to about 1.0. In some embodiments, the
engineered fuel feed stock has an O/C ratio from about 0.1 to about
0.8. In some embodiments, the engineered fuel feed stock has an O/C
ratio from about 0.2 to about 0.7. In some embodiments, the
engineered fuel feed stock has an O/C ratio from about 0.3 to about
0.6. In some embodiments, the engineered fuel feed stock has an O/C
ratio from about 0.4 to about 0.5. In some embodiments, the
engineered fuel feed stock has an O/C ratio of about 0.9. In some
embodiments, the engineered fuel feed stock has an O/C ratio of
about 0.01.
In some embodiments, the engineered fuel feed stock upon
gasification at 850.degree. C. and an ER of 0.34 produces synthesis
gas comprising H.sub.2 in an amount from about 6 vol. % to about 30
vol. %; CO in an amount from about 14 vol. % to about 25 vol. %,
CH.sub.4 in an amount from about 0.3 vol. % to about 6.5 vol. %,
CO.sub.2 in an amount from about 6.5 vol. % to about 13.5% vol. %;
and N.sub.2 in an amount from about 44 vol. % to about 68 vol.
%.
In some embodiments, the engineered fuel feed stock upon
gasification at 850.degree. C. and an ER of 0.34 produces synthesis
gas having an H.sub.2/CO ratio from about 0.3 to about 2.0. In some
embodiments, the engineered fuel feed stock upon gasification at
850.degree. C. and an ER of 0.34 produces synthesis gas having an
H.sub.2/CO ratio from about 0.5 to about 1.5. In some embodiments,
the engineered fuel feed stock upon gasification at 850.degree. C.
and an ER of 0.34 produces synthesis gas having an H.sub.2/CO ratio
from about 0.8 to about 1.2. In some embodiments, the engineered
fuel feed stock upon gasification at 850.degree. C. and an ER of
0.34 produces synthesis gas having an H.sub.2/CO ratio of about
1.0.
In some embodiments, the engineered fuel feed stock upon
gasification at 850.degree. C. and an ER of 0.34 produces synthesis
gas having H.sub.2 in an amount of about 20 vol. %; N.sub.2 in an
amount of about 46 vol. %; CO in an amount of about 25 vol. %;
CH.sub.4 in an amount of about 1 vol. %; CO.sub.2 in an amount of
about 8 vol. %; and a BTU/scf of about 160.
In some embodiments, the engineered fuel feed stock when combusted
produces less harmful emissions as compared to the combustion of
coal. In some embodiments, the engineered fuel feed stock when
combusted produces less sulfur emission as compared to the
combustion of coal. In some embodiments, the engineered fuel feed
stock when combusted produces less HCl emission as compared to the
combustion of coal. In some embodiments, the engineered fuel feed
stock when combusted produces less heavy metal emissions such as
for example mercury as compared to the combustion of coal. In some
embodiments, the engineered fuel feed stock is designed to avoid
the emission of particulate matters, NOx, CO, CO2, volatile organic
compounds (VOCs), and halogen gases.
In some embodiments, the engineered fuel feed stock is designed to
have reduced emission profiles with respect to GHGs as compared to
the GHGs emitted from combusted coal. In some embodiments, the
engineered fuel feed stock is designed to have reduced emission
profiles with respect to GHGs emitted from the combustion of
biomasses such as for example, wood, switch grass and the like.
In some embodiments, the feed stock is in a loose, non-densified
form. In other embodiments, the engineered fuel feed stock is in a
densified form. In some embodiments, the densified form is a cube.
In some embodiments, the densified form is rectangular. In other
embodiments, the densified form is cylindrical. In some
embodiments, the densified form is spherical. In some embodiments,
the densified form is a briquette. In other embodiments, the
densified form is a pellet. In some embodiments, the densified fuel
is sliced into sheets of different thickness. In some embodiments,
the thickness is between about 3/16 inches to about 3/4 inches. In
some embodiments, the engineered fuel feed stock further comprises
at least one waste material in addition to the component derived
from a processed MSW waste stream that enhances the gasification of
the fuel pellet. In some embodiments, the engineered fuel feed
stock further comprises at least one waste material in addition to
the component derived from a processed MSW waste stream that
enhances the gasification of the fuel pellet. In some embodiments,
the enhancement is a reduction in ash. In other embodiments, the
enhancement aids in the control of temperature. In still other
embodiments, the enhancement is a reduction in the amount of sulfur
emissions produced. In still other embodiments, the enhancement is
the reduction of chlorine emissions produced. In still other
embodiments, the enhancement is the reduction of heavy metal
emissions produced.
In some embodiments, the engineered fuel feed stock is rendered
inert. In some embodiments, the engineered fuel feed stock
comprises at least one additive that renders the feed stock inert.
In some embodiments, an additive can be blended into the processed
MSW waste stream that can render the resulting pellet inert. Some
types of wet MSW contain a relatively high number of viable
bacterial cells that can generate heat and hydrogen gas during
fermentation under wet conditions, for example during prolonged
storage or transportation. For example, an additive such as calcium
hydroxide can be added to the MSW for the prevention of the rotting
of food wastes and for the acceleration of drying of solid wastes.
In some embodiments, the additive that renders the feed stock inert
is CaO. Other non limiting examples of additives are calcium
sulfoaluminate and other sulfate compounds, as long as they do not
interfere with the downstream processes in which the pellet are
used.
Alternatively, the MSW can be rendered biologically inert through
any known method for inactivating biological material. For example,
X-rays can be used to deactivate the MSW before processing, or
after processing. Drying can be used to remove the water necessary
for organisms such as microbes to grow. Treatment of the MSW with
high heat and optionally also high heat under pressure
(autoclaving) will also render the MSW biologically inert. In one
embodiment, the excess heat generated by the reciprocating engines
or turbines fueled by the engineered pellets can be redirected
through the system and used to render the MSW inert. In other
embodiments, the feed stock is rendered inert through means such as
microwave radiation.
In some embodiments, the densified form of the engineered fuel feed
stock has a diameter of between about 0.25 inches to about 1.5
inches. In some embodiments, the densified form of the engineered
fuel feed stock has a length of between about 0.5 inches to about 6
inches. In some embodiments, the densified form of the engineered
fuel feed stock has a surface to volume ratio of between about 20:1
to about 3:1. In some embodiments, the densified form of the
engineered fuel feed stock has a bulk density of about 10
lb/ft.sup.3 to about 75 lb/ft.sup.3. In some embodiments, the
densified form of the engineered fuel feed stock has a porosity of
between about 0.2 and about 0.6. In some embodiments, the densified
form of the engineered fuel feed stock has an aspect ratio of
between about 1 to about 10. In some embodiments, the densified
form of the engineered fuel feed stock has a thermal conductivity
of between about 0.023 BTU/(fthr.degree. F.) and about 0.578
BTU/(fthr.degree. F.). In some embodiments, the densified form of
the engineered fuel feed stock has a specific heat capacity of
between about 4.78.times.10.sup.-5 BTU/(lb.degree. F.) to
4.78.times.10.sup.-4 BTU/(lb.degree. F.). In some embodiments, the
densified form of the engineered fuel feed stock has a thermal
diffusivity of between about 1.08.times.10.sup.-5 ft.sup.2/s to
2.16.times.10.sup.-5 ft.sup.2/s.
In some embodiments, the at least one waste material that enhances
the gasification of the fuel pellet is selected from fats, oils and
grease (FOG). In some embodiments, the at least one waste material
that enhances the gasification of the fuel pellet is sludge. In
some embodiments, the densified form of the engineered fuel feed
stock is substantially encapsulated within the FOG component. In
some of the embodiments, the encapsulation layer is scored. In
still further embodiments, the scoring of the encapsulated
densified form of the engineered fuel feed stock causes the fuel to
devolatize more efficiently during gasification process than the
fuel without the scoring.
In another aspect, an engineered fuel feed stock having a carbon
content of between about 30% and about 80%, a hydrogen content of
between about 3% and about 10%, a moisture content of between about
10% and about 30%, an ash content of less than about 10%, a sulfur
content of less than 2%, and a chlorine content of less than about
1% is described that is produced by a process comprising: a)
receiving a plurality of MSW waste feeds at a material recovery
facility; b) inventorying the components of the plurality of MSW
waste feeds of step a) as they pass through a material recovery
facility based on the chemical molecular characteristics of the
components; c) comparing the chemical molecular characteristics of
the components of the plurality of MSW waste feeds inventoried in
step b) with the chemical molecular characteristics of the
engineered fuel feed stock; d) optionally adding additional
engineered fuel feed stock components which contain chemical
molecular characteristics, whose sum together with the inventoried
components of step b) equal the chemical molecular characteristics
of the engineered fuel feed stock. In some embodiments, the feed
stock has a HHV of between about 3,000 BTU/lb and about 15,000
BTU/lb. In some embodiments, the feed stock has a volatile matter
content of about 40% to about 80%. In some embodiments, the
engineered fuel feed stock is reduced in size in order to
homogenize the feed stock. In some embodiments, the engineered fuel
feed stock is densified. In some embodiments, the densified feed
stock is in the form of a briquette. In some embodiments, the
densified feed stock is in the form of a pellet. In some
embodiments, the densified feed stock is in the form of a cube.
In another aspect, an engineered fuel feed stock is described that
is produced by a process comprising: a) separating a plurality of
MSW waste feeds at a material recovery facility into a plurality of
MSW waste components based on chemical molecular characteristics;
b) selecting chemical molecular characteristics for the engineered
fuel feed stock comprising a carbon content of between about 30%
and about 80%, a hydrogen content of between about 3% and about
10%, a moisture content of between about 10% and about 30%, an ash
content of less than about 10%, a sulfur content of less than 2%,
and a chlorine content of less than about 1% for the engineered
fuel feed stock; c) selecting MSW waste components from step a)
whose sum of chemical molecular characteristics equals the chemical
molecular characteristics selected in step b); d) optionally adding
other fuel components to the selections of step c) if the chemical
molecular characteristics of the MSW waste components selected in
step c) do not equal the chemical molecular characteristics of the
selection of step b); and e) mixing the components of step c) and
optionally of step d).
In some embodiments, the size of the mixture of step e) is reduced
to help homogenize the engineered fuel feed stock. In some
embodiments, a size and shape is determined for a densified form of
the mixture of step e) or the size-reduced mixture of step e). In
some embodiments, the mixture of step e) is densified. In other
embodiments, the size-reduced mixture of step e) is densified. In
some embodiments, the engineered fuel feed stock has a HHV of
between about 3,000 BTU/lb and about 15,000 BTU/lb. In some
embodiments, the feed stock has a volatile matter content of about
40% to about 80%.
In another aspect, a method of producing an engineered fuel feed
stock from a processed MSW waste stream is described which
comprises the steps of:
a) selecting a plurality components from a processed MSW waste
stream which components in combination have chemical molecular
characteristics comprising a carbon content of between about 30%
and about 80%, a hydrogen content of between about 3% and about
10%, a moisture content of between about 10% and about 30%, an ash
content of less than 10%, and a sulfur content of less than 2%; b)
combining and mixing together the selected components of step a) to
form a feed stock; c) comparing the resulting chemical molecular
characteristics of the feed stock of step b) with the chemical
molecular characteristics of step a); d) optionally adding other
fuel components to the selected components of step b) if the
chemical molecular characteristics of the MSW waste components
selected in step b) do not equal the chemical molecular
characteristics of step a).
In some embodiments, the size of the mixture of step b) or step d)
is reduced to help homogenize the engineered fuel feed stock. In
some embodiments, a size and shape is determined for a densified
form of the mixture of step b) or the size-reduced mixtures of
steps b) or d). In some embodiments, the mixture of step b) is
densified. In other embodiments, the size-reduced mixture of step
e) is densified to a density of about 10 lbs/ft.sup.3 to about 75
lbs/ft.sup.3. In some embodiments, the engineered fuel feed stock
has a HHV of between about 3,000 BTU/lb and about 15,000 BTU/lb. In
some embodiments, the feed stock has a volatile matter content of
about 40% to about 80%.
In another aspect, a method of producing a engineered fuel feed
stock is described, the method comprising: a) receiving a plurality
of MSW waste streams; b) selecting for the engineered fuel feed
stock chemical molecular characteristics comprising a carbon
content of between about 30% and about 80%, a hydrogen content of
between about 3% and about 10%, a moisture content of between about
10% and about 30%, an ash content of less than 10%, and a sulfur
content of less than 2%; c) inventorying the components of the
plurality of MSW waste streams based on the chemical molecular
characteristics of the components; d) comparing the chemical
molecular characteristics of the inventoried components of the
plurality of MSW waste streams of step c) with the selected
chemical molecular characteristics of step b); and e) optionally
adding additional fuel components with the required chemical
molecular characteristics to inventoried components of step c) to
meet the desired chemical molecular characteristics of step b) for
the engineered fuel feed stock. In some embodiments, the engineered
fuel feed stock of steps c) or e) is mixed. In some embodiments,
the engineered fuel feed stock of steps c) or e) is reduced in
size. In some embodiments, the engineered fuel feed stock of steps
c) or e) are densified. In some embodiments, the size-reduced
engineered fuel feed stock of steps c) or e) are densified. In some
embodiments, the engineered fuel feed stock is densified to about
10 lbs/ft.sup.3 to about 75 lbs/ft.sup.3.
In some embodiments, the engineered fuel feed stock is densified to
form a briquette. In other embodiments, the engineered fuel feed
stock is densified to form of a pellet.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by the embodiments shown in
the drawings, in which:
FIG. 1 shows commonly available feed stock materials, such as, for
example, coal, FOGs, wood, sludge, black liquor, rubber and MSW
streams, positioned in terms of their hydrogen content to carbon
content ratio (H/C) (lb/lb) and oxygen content to carbon content
(O/C) (lb/lb) ratio.
FIG. 2 shows some novel engineered fuel feed stocks produced by
selecting known engineered fuel feed stocks within the dotted line
and directly mixing the selected feed stocks, and in some cases
increasing or decreasing the moisture content.
FIG. 3 shows a schematic with direct combustion of feed stock.
FIG. 4 shows a schematic with direct combustion of wet feed stock,
without reducing its moisture content.
FIG. 5 shows the predicted effect of moisture on gasification
temperature, carbon conversion and H.sub.2+CO production rate for a
typical coal feed stock at a constant air equivalence (ER) ratio
(ER=0.34).
FIG. 6 shows the predicted variation of syngas compositions with
feed stocks of different moisture contents for a typical wood feed
stock at 800.degree. C.
FIG. 7 shows the predicted effect of fuel moisture content on
carbon conversion, cold gas efficiency and CO+H.sub.2 production
rate for a typical coal feed stock at 850.degree. C.
FIG. 8 shows the predicted effect of fuel moisture content on
carbon conversion, cold gas efficiency and CO+H.sub.2 production
rate for pure carbon at 1000.degree. C.
FIG. 9 shows the predicted total and external water supply required
to produce a syngas of H.sub.2/CO=2.0 at 850.degree. C. for a
typical wood feed stock.
FIG. 10 shows the predicted CO+H.sub.2 production rate, cold gas
efficiency and H.sub.2/CO ratio at 850.degree. C. and an ER=0.30
for a typical wood feed stock.
FIG. 11 provides a graphical representation of eq. 2 showing the
weight fraction of various products as a function of the chain
growth parameter .alpha..
FIG. 12 provides predicted C/H and C/O ratios needed in feed stock
for the production of syngas with varying H.sub.2/CO ratios.
FIG. 13 provides a graph showing cylindrical diameter plotted
against the sphericity, the cylindrical length and specific
area.
FIG. 14 provides a graph of feed stock containing different carbon
and hydrogen contents and their predicted production of CO and
H.sub.2 during air gasification.
FIG. 15 provides a graph of feed stock containing different carbon
and hydrogen contents and their predicted production of CO and
H.sub.2 during air/steam gasification.
DETAILED DESCRIPTION OF THE INVENTION
Novel engineered fuel feed stocks are provided that comprise at
least one waste stream component derived from MSW, such as
recycling residue which is the non-recoverable portion of
recyclable materials, and which are engineered to have
predetermined chemical molecular characteristics. These feed stocks
can possess the chemical molecular characteristics of biomass fuels
such as, for example, wood and switch grass, and, can also have the
positive characteristics of high BTU containing fuels such as, for
example, coal, without the negative attributes of coal such as
deleterious sulfur emissions. Also described are novel engineered
fuel feed stocks that comprise chemical molecular characteristics
not observed in natural fuels such as, for example, biomass, coal,
or petroleum fuels. These novel fuels contain, for example, unique
ratios of carbon, hydrogen, sulfur, and ash, such that, when
compared to known fuels, they provide a different combustion or
gasification profile. Since these novel feed stocks have different
combustion or gasification profiles, they provide novel fuels for
many different types of combustors and gasifiers which, while
functioning adequately due to the uniformity of the natural fuel,
do not function optimally due to the less than optimized chemical
molecular characteristics of natural fuels. Engineered fuel feed
stocks such as those useful for the production of thermal energy,
power, biofuels, petroleum, and chemicals can be engineered and
synthesized according to the methods disclosed herein.
Highly variable and heterogeneous streams of waste can now be
processed in a controlled manner and a plurality of the resulting
components therefrom recombined into an engineered fuel feed stock
which behaves as a constant and homogeneous fuel for use in
subsequent conversion processes. Included among these processes are
pyrolysis, gasification and combustion. The engineered fuel feed
stock can be used alone to produce thermal energy, power, biofuels,
or chemicals, or it can be used as a supplement along with other
fuels for these and other purposes. Methods and processes for
engineering homogeneous engineered fuel feed stock from naturally
heterogeneous and variable waste streams which possess a variety of
optimal physical and chemical characteristics for different
conversion processes are described, as well as different feed
stocks themselves.
Chemical properties can be engineered into the resulting engineered
fuel feed stocks based on the type of conversion process for which
the fuel will be used. Feed stocks can be engineered for use as
fuels including synthetic fuels, high BTU containing fuels (HHV
fuels) and fuels useful to produce high quality syngas, among other
types of useful fuels. For example, engineered fuels can be
designed to have the same or similar chemical molecular
compositions as known solid fuels, such as, for example, wood,
coal, coke, etc. and function as a substitute for, or supplemental
to, fuel for combustion and gasification. Other fuels can be
designed and synthesized which have chemical molecular
characteristics that are different than naturally occurring fuel.
For example, High BTU Fuels can be designed to have the highest
possible heat content with a tolerable ash content in order to
prevent slagging. These fuels have comparable energy density (such
as carbon content, hydrogen content) as coal, but without the
problems of slagging, fusion and sulfur pollution (ash content,
sulfur content, and chlorine content) and can serve as a substitute
for coal, or a supplement to coal. Fuels can be designed to produce
high quality syngas by optimizing, for example, the content of C,
H, O, moisture, and ash in the engineered fuel feed stock. Such
fuels produce high quality syngas in terms of, for example, syngas
caloric value, H.sub.2/CO ratios, and amounts of CO, H.sub.2,
CO.sub.2, and CH.sub.4. These fuels that produce high quality
syngas enable the stable operation of gasifiers due to no, or
minimal, slag formation and the lowest tar formation (at the
appropriate gasifier temperatures). Thermal conversion devices are
described in the art which are designed to suit specific fuels
found in the nature and in these cases operational problems often
occur or modifications are needed to the devices when fuels other
than the designed for fuels are co-fired. The present invention
provides for an optimal fuel to be engineered that will best suit
known thermal conversion devices and no modifications to the device
will be needed.
The engineered fuel feed stock described herein provides an
efficient way to moderate the operating conditions of thermal
conversion devices such as for example by lower the operating
temperature, by reducing the need for oxygen supply or steam
supply, by allowing for the relaxing of emission controls. The
methods described herein provide a powerful means for upgrading
low-grade fuels such as sludge, yardwastes, food wastes and the
like to be transformed into a high quality fuel.
The following specification describes the invention in greater
detail.
DEFINITIONS
The term "air equivalence ratio" (ER) means the ratio of the amount
of air supplied to the gasifier divided by the amount of air
required for complete fuel combustion. Air equivalence ratio, "ER,"
can be represented by the following equation:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times.
##EQU00001##
The term "British Thermal Unit" (BTU) means the amount of heat
energy needed to raise the temperature of one pound of water by one
degree F.
The term "carbon boundary" means the temperature obtained when
exactly enough oxygen is added to achieve complete gasification, or
carbon conversion. Above this temperature there is no solid carbon
present.
The term "carbon content" means all carbon contained in the fixed
carbon (see definition below) as well as in all the volatile
matters in the feed stock.
The term "carbon conversion" means to convert solid carbon in fuel
feed stock into carbon-containing gases, such as CO, CO2 and CH4 in
most gasification operations
The term "commercial waste" means solid waste generated by stores,
offices, restaurants, warehouses, and other non-manufacturing,
non-processing activities. Commercial waste does not include
household, process, industrial or special wastes.
The term "construction and demolition debris" (C&D) means
uncontaminated solid waste resulting from the construction,
remodeling, repair and demolition of utilities, structures and
roads; and uncontaminated solid waste resulting from land clearing.
Such waste includes, but is not limited to bricks, concrete and
other masonry materials, soil, rock, wood (including painted,
treated and coated wood and wood products), land clearing debris,
wall coverings, plaster, drywall, plumbing fixtures, nonasbestos
insulation, roofing shingles and other roof coverings, asphaltic
pavement, glass, plastics that are not sealed in a manner that
conceals other wastes, empty buckets ten gallons or less in size
and having no more than one inch of residue remaining on the
bottom, electrical wiring and components containing no hazardous
liquids, and pipe and metals that are incidental to any of the
above. Solid waste that is not C&D debris (even if resulting
from the construction, remodeling, repair and demolition of
utilities, structures and roads and land clearing) includes, but is
not limited to asbestos waste, garbage, corrugated container board,
electrical fixtures containing hazardous liquids such as
fluorescent light ballasts or transformers, fluorescent lights,
carpeting, furniture, appliances, tires, drums, containers greater
than ten gallons in size, any containers having more than one inch
of residue remaining on the bottom and fuel tanks. Specifically
excluded from the definition of construction and demolition debris
is solid waste (including what otherwise would be construction and
demolition debris) resulting from any processing technique, that
renders individual waste components unrecognizable, such as
pulverizing or shredding.
The term "devolatization" means a process that removes the volatile
material in a engineered fuel feed stock thus increasing the
relative amount of carbon in the engineered fuel feed stock.
The term "fixed carbon" is the balance of material after moisture,
ash, volatile mater determined by proximate analysis.
The term "garbage" means putrescible solid waste including animal
and vegetable waste resulting from the handling, storage, sale,
preparation, cooking or serving of foods. Garbage originates
primarily in home kitchens, stores, markets, restaurants and other
places where food is stored, prepared or served.
The term "gasification" means a technology that uses a
noncombustion thermal process to convert solid waste to a clean
burning fuel for the purpose of generating for example,
electricity, liquid fuels, and diesel distillates. Noncombustion
means the use of no air or oxygen or substoichiometric amounts of
oxygen in the thermal process.
The term "hazardous waste" means solid waste that exhibits one of
the four characteristics of a hazardous waste (reactivity,
corrosivity, ignitability, and/or toxicity) or is specifically
designated as such by the Environmental Protection Agency (EPA) as
specified in 40 CFR part 262.
The term "Heating Value" is defined as the amount of energy
released when a fuel is burned completely in a steady-flow process
and the products are returned to the state of the reactants. The
heating value is dependent on the phase of water in the combustion
products. If H.sub.2O is in liquid form, heating value is called
HHV (Higher Heating Value). When H.sub.2O is in vapor form, heating
value is called LHV (Lower Heating Value).
The term "higher heating value" (HHV) means the caloric value
released with complete fuel combustion with product water in liquid
state. On a moisture free basis, the HHV of any fuel can be
calculated using the following equation:
HHV.sub.Fuel=146.58C+568.78H+29.4S-6.58A-51.53(O+N). wherein C, H,
S, A, O and N are carbon content, hydrogen content, sulfur content,
ash content, oxygen content and nitrogen content, respectively, all
in weight percentage.
The term "municipal solid waste" (MSW) means solid waste generated
at residences, commercial or industrial establishments, and
institutions, and includes all processable wastes along with all
components of construction and demolition debris that are
processable, but excluding hazardous waste, automobile scrap and
other motor vehicle waste, infectious waste, asbestos waste,
contaminated soil and other absorbent media and ash other than ash
from household stoves. Used tires are excluded from the definition
of MSW. Components of municipal solid waste include without
limitation plastics, fibers, paper, yard waste, rubber, leather,
wood, and also recycling residue, a residual component containing
the non-recoverable portion of recyclable materials remaining after
municipal solid waste has been processed with a plurality of
components being sorted from the municipal solid waste.
The term "nonprocessable waste" (also known as noncombustible
waste) means waste that does not readily gasify in gasification
systems and does not give off any meaningful contribution of carbon
or hydrogen into the synthesis gas generated during gasification.
Nonprocessable wastes include but are not limited to: batteries,
such as dry cell batteries, mercury batteries and vehicle
batteries; refrigerators; stoves; freezers; washers; dryers;
bedsprings; vehicle frame parts; crankcases; transmissions;
engines; lawn mowers; snow blowers; bicycles; file cabinets; air
conditioners; hot water heaters; water storage tanks; water
softeners; furnaces; oil storage tanks; metal furniture; propane
tanks; and yard waste.
The term "processed MSW waste stream" means that MSW has been
processed at, for example, a materials recovery facility, by having
been sorted according to types of MSW components. Types of MSW
components include, but are not limited to, plastics, fibers,
paper, yard waste, rubber, leather, wood, and also recycling
residue, a residual component containing the non-recoverable
portion of recyclable materials remaining after municipal solid
waste has been processed with a plurality of components being
sorted from the municipal solid waste. Processed MSW contains
substantially no glass, metals, grit, or non-combustibles. Grit
includes dirt, dust, granular wastes such as coffee grounds and
sand, and as such the processed MSW contains substantially no
coffee grounds.
The term "processable waste" means wastes that readily gasify in
gasification systems and give off meaningful contribution of carbon
or hydrogen into the synthesis gas generated during gasification.
Processable waste includes, but is not limited to, newspaper, junk
mail, corrugated cardboard, office paper, magazines, books,
paperboard, other paper, rubber, textiles, and leather from
residential, commercial, and institutional sources only, wood, food
wastes, and other combustible portions of the MSW stream.
The term "pyrolysis" means a process using applied heat in an
oxygen-deficient or oxygen-free environment for chemical
decomposition of solid waste.
The term "recycling residue" means the residue remaining after a
recycling facility has processed its recyclables from incoming
waste which no longer contains economic value from a recycling
point of view.
The term "sludge" means any solid, semisolid, or liquid generated
from a municipal, commercial, or industrial wastewater treatment
plant or process, water supply treatment plant, air pollution
control facility or any other such waste having similar
characteristics and effects.
The term "solid waste" means unwanted or discarded solid material
with insufficient liquid content to be free flowing, including but
not limited to rubbish, garbage, scrap materials, junk, refuse,
inert fill material, and landscape refuse, but does not include
hazardous waste, biomedical waste, septic tank sludge, or
agricultural wastes, but does not include animal manure and
absorbent bedding used for soil enrichment or solid or dissolved
materials in industrial discharges. The fact that a solid waste, or
constituent of the waste, may have value, be beneficially used,
have other use, or be sold or exchanged, does not exclude it from
this definition.
The term "steam/carbon ratio" (S/C) means the ratio of total moles
of steam injected into the gasifier/combustor divided by the total
moles of carbon feed stock. The steam/carbon ratio, "S/C," can be
represented by the following equation:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times.
##EQU00002##
The term "thermal efficiency" (also known as cold gas efficiency)
means the ratio of the total HHV contained in the resulting product
gas divided by the total HHV that was contained in the fuel input.
Thermal efficacy, "Eff," can be represented by the following
equation:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times. ##EQU00003##
The term "volatile materials" (also known as volatile organic
compounds) means the organic chemical compounds that have high
enough vapor pressures under normal conditions to significantly
vaporize and enter the atmosphere. Non-limiting examples of
volatile materials include aldehydes, ketones, methane, and other
light hydrocarbons.
Described herein are novel engineered fuel feed stocks comprising
MSW, the feed stocks having any of a number of desired chemical
molecular characteristics, including but not limited to carbon
content, hydrogen content, oxygen content, nitrogen content, ash
content, sulfur content, moisture content, chlorine content, and
HHV content. This feed stock is useful for a variety of chemical
conversion processes. Also described are processes for producing an
engineered fuel feed stock and methods of making same.
One abundant source of engineered fuel feed stock is MSW. MSW is
solid waste generated at residences, commercial or industrial
establishments, and institutions, and includes all processable
wastes along with all components of construction and demolition
debris that are processable, but excluding hazardous waste,
automobile scrap and other motor vehicle waste, infectious waste,
asbestos waste, contaminated soil and other absorbent media and ash
other than ash from household stoves. It does include garbage,
refuse, and other discarded materials that result from residential,
commercial, industrial, and community activities. The composition
of MSW varies widely depending on time of collection, season of the
year of collection, the types of customers from which the MSW is
collected on any given day, etc. MSW may contain a very wide
variety of waste or discarded material. For instance, the waste may
include biodegradable waste, non-biodegradable waste, ferrous
materials, non-ferrous metals, paper or cardboard in a wide variety
of forms, a wide range of plastics (some of which may contain
traces of toxic metals used as catalysts, stabilizers or other
additives), paints, varnishes and solvents, fabrics, wood products,
glass, chemicals including medicines, pesticides and the like,
solid waste of various types and a wide range of other materials.
The waste includes household waste and industrial waste. Industrial
waste contemplated for use herein is low in toxic or hazardous
materials. However, MSW is processed in order to remove
non-processable components prior to engineering the engineered fuel
feed stocks described herein.
Processed MSW has been sorted or inventoried according to types of
MSW components. Types of MSW components include, but are not
limited to, plastics, fibers, paper, yard waste, rubber, leather,
wood, and also recycling residue, a residual component containing
the non-recoverable portion of recyclable materials remaining after
municipal solid waste has been processed with a plurality of
components being sorted from the municipal solid waste. Processed
MSW contains substantially no glass, metals, grit, or
non-combustibles. Grit includes dirt, dust, granular wastes such as
coffee grounds and sand, and as such the processed MSW contains
substantially no coffee grounds. The term "substantially no" as
used herein means that no more than 0.01% of the material is
present in the MSW components.
Another fuel source for use in an engineered fuel feed stock is
FOGs. FOGs are commonly found in such things as meats, sauces,
gravy, dressings, deep-fried foods, baked goods, cheeses, butter
and the like. Many different businesses generate FOG wastes by
processing or serving food, including; eating and drinking
establishments, caterers, hospitals, nursing homes, day care
centers, schools and grocery stores. FOGs have been a major problem
for municipalities. Studies have concluded that FOGs are one of the
primary causes of sanitary sewer blockages which result in sanitary
sewer system overflows (SSOs) from sewer collection systems. These
SSOs have caused numerous problems in some municipalities including
overflow out of the sewage lines out of maintenance (manhole) holes
and into storm drains. The water in storm drains flows into the
water ways and eventually into the ocean. SSOs pose a threat to
public health, adversely affect aquatic life, and are expensive to
clean up. The most prevalent cause of the SSOs is FOG accumulation
in the small to medium sewer lines serving food service
establishments. Thus a use as fuel would provide a means of
disposal of FOGs without the prevalence of SSOs occurring due to
the discharge of FOGs into the waste water.
Present methods of discarding FOGs, besides directly into the sewer
systems, include landfills. While these types of wastes are
generally considered nuisances, they contain a high carbon content
that can be transformed into a source of fuel.
Other types of oils and greases useful in the present invention are
petroleum waste products. Nonlimiting examples of petroleum waste
products include discarded engine oil.
Yet another type of waste useful in the production of engineered
fuel feed stock is biomass waste, also known as biogenic waste.
Biomass refers to living and recently dead biological material that
can be used as fuel or for industrial production. Most commonly,
biomass refers to plant matter grown for use as biofuel, but it
also includes plant or animal matter used for production of fibers,
chemicals or heat. Biomass may also include biodegradable wastes
that can be burnt as fuel. It excludes organic material which has
been transformed by geological processes into substances such as
coal or petroleum. Nonlimiting types of biomass waste include
woods, yard wastes, plants, including miscanthus, switchgrass,
hemp, corn, poplar, willow, sugarcane and oil palm (palm oil),
coconut shells, and shells of nuts.
Yet another type of waste useful in the production of engineered
fuel feed stock is sludge. Sludge is a mixture of solid wastes and
bacteria removed from the wastewater at various stages of the
treatment process. It can be categorized as "primary sludge" and
"secondary sludge". Primary sludge is about 4% solids and 96%
water. It consists of the material which settles out of wastewater
in the primary sedimentation tanks, before bacterial digestion
takes place. Secondary or activated sludge is much more
liquid--about 1% solids and 99% water. Secondary sludge consists of
bacteria and organic materials on which the bacteria feed. About
30% of the secondary sludge produced is returned to the aeration
tanks to assist with the biological process of sewage treatment.
The remaining 70% must be disposed of.
The sludge contemplated for use in the present invention is
municipal sludge a.k.a. biosolids. Municipal sludge does not
include papermill or other industrial/agricultural sludge. The key
determinants of the caloric or BTU value of a sludge are its
dryness expressed as Total Solids on a wet weight basis (or
inversely as water content) and its volatile solids content (Total
Volatile Solids or TVS expressed on a dry weight basis). There are
two distinct types of sludge--1) raw sludge (sludge treated only
with primary and secondary aerobic clarifiers) and 2) digested
sludge (add anaerobic digestion to number 1). Anaerobic sludge is
typically 60% TVS and raw sludge is typically 75-80% TVS. The TS of
sludge cake (dewatered sludge) varies depending on the method used
by the treatment plant to dewater the sludge, and ranges from 10%
to 97+%. One pound of Volatile Solids has about 10,000-12,000 BTU,
e.g., it requires 1,200 BTU to drive off 1 lb of water as
steam.
Other types of materials useful in the production of engineered
feed stocks described herein are animal wastes such as manures,
animal biomass (meat and bone tissue), poultry litter, fossil fuels
such as coal, coal by products, petroleum coke, black liquor, and
carbon black.
Chemical compositions of fuel are known to affect reactor
performance, whether for combustion or gasification, and therefore
the production of, and quality of, syngas. Most gasifiers are
constructed so as to be able to efficiently burn one type of
fuel--a homogeneous fuel, such as wood pellets or coal, for
example. Although the natural fuels such as wood or coal are
homogeneous and provide the reactor with a constant supply of
predictable fuel, these fuels do not allow the reactors to function
optimally due to their suboptimal chemical molecular
characteristics.
Furthermore, syngas, which results from the gasification process,
can be used to produce, for example, diesel distillates and liquid
fuels. Syngas useful in the production of such products should
contain at least a certain amount energy expressed usually in
BTU/ft.sup.3 in order to be used efficiently in liquid fuel
production, while other syngas requirements for this process may
also include an appropriate ratio of hydrogen to carbon monoxide
(H.sub.2/CO), as well as syngas purity.
Engineered fuel feed stock is described herein which comprises at
least one component derived from a processed MSW waste stream and
embodies predetermined chemical molecular characteristics that
cause the fuel to perform optimally for a particular thermal
conversion process. By selecting waste components from MSW so as to
remove contaminating wastes that do not contribute to the
gasification process or create hazardous emissions (such as
dioxins, mercury, sulfur and chlorine, etc.), and optionally adding
other materials that enhance the gasification or combustion
process, material useful for production of engineered fuel feed
stock with the appropriate chemical molecular characteristics is
achieved.
FIG. 1 shows commonly available feed stock materials, such as, for
example, coal, FOGs, wood, sludge, black liquor, rubber and MSW
streams, positioned in terms of their hydrogen content to carbon
content ratio (H/C) (lb/lb) and oxygen content to carbon content
(O/C) (lb/lb) ratio. When these natural feed stocks are surrounded
on the graph by a solid line, an envelope is formed, which
indicates the range of H/C and O/C for naturally occurring
materials. FIG. 1 also plotted the carbon boundary temperature
against the O/C ratio, with variations with H/C indicated by a
slashed area. The carbon boundary temperature is the temperature
obtained when exactly enough oxygen is added to achieve complete
carbon conversion. For biomass gasification the typical temperature
is about 850.degree. C. and for dry coal gasification the typical
temperature is about 1,500.degree. C. Fuels such as anthracite,
semianthracite, high- and low-volatile bituminous all have low H/C
ratios from about 0.03 to 0.07 and low O/C content ratios from
about 0.05 to about 0.12. These fuels require high temperatures due
to the low O/C ratio and normally require steam injection to
promote complete conversion of the carbon during gasification.
Other feed stocks such as various woods, magazines, mixed paper,
and corrugated cardboard all have relatively high H/C content
ratios of about 0.1 to about 0.14 and O/C content ratios of about
0.8 to about 1.0, which in practice require low gasification
temperatures. For feed stocks to be fully gasified at about
850.degree. C., it is seen from FIG. 1 that the O/C ratio in feed
stock should be about 0.55 to 0.6. For woody biomass feed stocks
which have a O/C ratio of about 0.75 to 0.90, over-oxidizing (or
increased oxidation) may occur at this temperature, and thus a
higher CO.sub.2 in the syngas would be expected. Therefore, it is
an advantage of the engineered feed stock that fuel O/C and H/C
ratios can be adjusted to allow for optimal gasification operation
and performance to be achieved.
In FIG. 1, it can also be observed that H.sub.2/CO production will
vary according to H/C content, but only slightly with increasing
O/C content. Also, FIG. 1 shows that Heating Value and H.sub.2+CO
production rate both increase with increasing H/C ratios and with
decreasing O/C ratios.
By judiciously selecting engineered fuel feed stocks based on, for
example, their H/C ratio, O/C ratio, ash content and moisture
content, the present inventors have discovered novel engineered
fuel feed stocks that can both simulate naturally occurring fuels,
such as for example wood and coal, as well as populate the carbon
boundary with heretofore unknown novel engineered fuel feed stocks
that have different gasification profiles as compared to known
engineered fuel feed stocks. FIG. 2 shows some novel engineered
fuel feed stocks produced by selecting known engineered fuel feed
stocks within the dotted line and directly mixing the selected feed
stocks, and in some cases increasing or decreasing the moisture
content. These novel feed stocks populate areas within the solid
lined area within the carbon temperature boundary. Engineered fuel
feed stock can be designed by selecting types of feed stock
characteristics identified within the carbon boundary of the graph
based on, for example, H.sub.2/CO content in the product syngas,
H.sub.2+CO production rate and Heating Value of the syngas, which
would indicate the H/C ratio and O/C ratio required for a
particular engineered fuel that should be best suited for a
particular application. For various applications, such as, for
example, gasification for energy production, gasification for
Fischer-Tropsch fuel production, pyrolysis, and combustion
different HHV contents, CO+H2 production rates or H.sub.2/CO ratios
may be required.
Chemical Properties of Fuel that Affect Gasification and Combustion
of the Fuel
The combustion and gasification processes use fuel containing
sufficient energy that upon firing the fuel releases the stored
chemical energy. This energy stored in the fuel can be expressed in
terms of percent carbon, hydrogen, oxygen, along with the effects
of other components such as sulfur, chlorine, nitrogen, and of
course moisture in the form of H.sub.2O.
As a possible fuel source, MSW can be characterized by its chemical
molecular make up, such as, for example, the amount of carbon,
hydrogen, oxygen, and ash present. However, MSW normally consists
of a variety of components that can individually or collectively be
characterized themselves for fuel purposes by a variety of
parameters including, without limitation, carbon content, hydrogen
content, moisture content, ash content, sulfur content, chlorine
content, and HHV content. Although heterogeneic in nature, the many
components of MSW can serve as raw materials for engineering
various engineered fuel feed stocks useful for a variety of
different thermal conversion processes. Such materials can be
engineered to create engineered fuel feed stocks that embody the
chemical characteristics of known fuels, for example, wood and
coal, while other feed stocks can be engineered to create fuels
that are not observed in nature and provide unique combustion and
gasification profiles. For example, the carbon and hydrogen content
of most biomasses such as wood is given in Table 1. From Table 1 it
can be readily observed that the range of carbon in biomass such as
wood varies only slightly, as does the hydrogen content.
TABLE-US-00001 TABLE 1 Name Vola- C H O N S Ash tiles HHV WOOD % %
% % % % % BTU/lb Beech 51.64 6.26 41.45 0.00 0.00 0.65 -- 8,762
Black 50.73 5.71 41.93 0.57 0.01 0.80 80.94 8,474 Locust Douglas
Fir 52.30 6.30 40.50 0.10 0.00 0.80 81.50 9,050 Hickory 47.67 6.49
43.11 0.00 0.00 0.73 -- 8,672 Maple 50.64 6.02 41.74 0.25 0.00 1.35
-- 8,581 Ponderosa 49.25 5.99 44.36 0.06 0.03 0.29 82.54 8,607 Pine
Poplar 51.64 6.26 41.45 0.00 0.00 0.65 -- 8,921 Red Alder 49.55
6.06 43.78 0.13 0.07 0.40 87.10 8,298 Redwood 53.50 5.90 40.30 0.10
0.00 0.40 83.50 9,041 Western 50.40 5.80 41.10 0.10 0.10 2.20 84.80
8,620 Hemlock Yellow Pine 52.60 7.00 40.10 0.00 0.00 1.31 -- 9,587
White Fir 49.00 5.98 44.75 0.05 0.01 0.25 83.17 8,577 White Oak
49.48 5.38 43.13 0.35 0.01 1.52 81.28 8,349 Madrone 48.94 6.03
44.75 0.05 0.02 0.20 87.80 8,388
Likewise the carbon content of most coals does not vary widely as
seen in Table 2, and most examples of coal have similar if not
identical carbon and hydrogen content.
TABLE-US-00002 TABLE 2 Name Heat Vola- content C H O S tiles BTU/lb
Lignite.sup.1 60-75 6.0-5.8 34-17 0.5-3 45-65 <12,240 Flame coal
75-82 6.0-5.8 >9.8 ~1 40-45 <14,130 Gas flame 82-85 5.8-5.6
9.8-7.3 ~1 35-40 <14,580 coal Gas coal 85-87.5 5.6-5.0 7.3-4.5
~1 28-35 <15,030 Fat coal 87.5-89.5 5.0-4.5 4.5-3.2 ~1 19-28
<15,210 Forge coal 89.5-90.5 4.5-4.0 3.2-2.8 ~1 14-19 <15,210
Non baking 90.5-91.5 4.0-3.7 2.8-3.5 ~1 10-14 <15,210 coal
Anthracite >91.5 <3.75 <2.5 ~1 7-12 <15,210
.sup.1Lindner, E., Chemie fur Ingenieure, Lindner Verlag Karlsruhe,
(2007) p. 258.
When used as a fuel source, for example, in gasification, the
carbon and hydrogen content have a significant effect on the
chemical characteristics of the syngas. Thus, because the carbon
and hydrogen content of, for example, wood does not vary greatly,
the process of gasification must be varied so that the chemical
characteristics of the syngas can be varied. In contrast, the
present invention allows engineered fuel feed stocks to be
engineered that not only contain the carbon content of wood or
coal, but also amounts of carbon and hydrogen not contained in
biomasses such as wood or in fuels such as coal, thereby providing
new fuels for gasification and combustion reactions. Thus, the
present invention provides for engineered fuel feed stocks to be
engineered to contain a variety of carbon and hydrogen amounts
beyond what is contained in naturally occurring fuels.
Effect of Feed Stock Moisture on Gasification and Combustion
Combustion Applications
It is generally true that as moisture content increases in feed
stock, the efficiency of the combustor or burner is reduced since
some part of the heat released from feed stock will be consumed by
evaporating the water. However, in order to understand the impact
of feed stock moisture on the efficiency of the combustion, an
overall systems perspective must be developed.
The prior art has understood that moisture should, if not, must be
reduced to low levels, such as below 10%, in order to have fuels
that will allow for efficient firing of combustion reactors (see
for example U.S. Pat. No. 7,252,691). However, consider a process
(FIG. 3) in which the wet fuel is first dried using an energy
stream Q.sub.1, which is generally equal to the heat needed for
vaporization of the water in the fuel and a sensible heat change
resulting from the difference between the feed stock inlet and
outlet temperatures, in addition to heat losses from the dryer.
After drying, the water vapor is vented and the feed stock with
reduced moisture content is sent to the combustor or boiler, where
a heating load Q.sub.2 is applied. The total net available energy
is then Q.sub.net=Q.sub.2-Q.sub.1, which represents the effect of
the additional energy needed from the entire system for reducing
the moisture content of the fuel.
By comparison, FIG. 4 shows a schematic with direct combustion of
wet feed stock, without reducing its moisture content. The
available heat utilization is Q.sub.3. In order to understand the
impact of moisture on the engineered fuel feed stock a simulation
using HYSYS (AspenTech, Inc., Burlington Mass.) was performed under
the following parameters. Feed stock with a moisture content of
either 30 wt % or 40 wt %, was dried at a rate of one tone per hour
to a moisture content of 10 wt %, i.e. 445 lbs/hr or 667 lbs/hr of
water removed (vaporized by heating to about 250.degree. F. This
requires an input of energy of approximately 0.64 mmBTU/hr or 0.873
mmBTU/hr, respectively. The feed stock at a moisture content of 10
wt % is then combusted in a boiler assuming the heating load is
adjusted to control the flue gas temperature to a predetermined
temperature. Depending on the boiler or heat exchanger design, this
predetermined temperature could be higher (non-condensation,
150.degree. F.) or lower (condensation, 100.degree. F.) than the
temperature of water in flue gas. The results are tabulated below
in Table 3 and Table 4:
TABLE-US-00003 TABLE 3 Process with feed stock Process w/o feed
stock drying drying Initial feed stock moisture (wt %) 30 30 Final
feed stock moisture 10 30 Water vapor removed (lb/h) 445 0 Heat
required for drying (mmBTU/h) 0.640 0 Heat utilization from boiler
9.571 (non-condensation) 8.972 (non-condensation) (mmBTU/h) 9.949
(condensation) 9.825 (condensation) Net heat utilization (mmBTU/h)
8.931 (non-condensation) 8.972 (non-condensation) 9.309
(condensation) 9.825 (non-condensation) Heat utilization efficiency
(%) 71.3 (non-condensation) 71.6 (non-condensation) 74.3
(condensation) 78.4 (condensation) Flue gas mass flow rate (lb/h)
12,642 13,087 Adiabatic flame temperature (.degree. F.) 2,725 2,445
Thermal equilibrium CO production 71 11 (ppm) Thermal equilibrium
NO.sub.x production 2,311 1,212 (ppm) Vapor content in flue gas (%)
8.9 13.8 CO.sub.2 in flue gas (%) 13.7 13.0 Assumptions: (1): the
feed stock is assumed to have properties similar to wood (2): the
combustion air is adjusted to have 8% O.sub.2 in flue gas.
TABLE-US-00004 TABLE 4 Process with feed stock Process w/o feed
stock drying drying Initial feed stock moisture (wt %) 40 40 Final
feed stock moisture 10 40 Water vapor removed (lb/h) 667 0 Heat
required for drying (mmBTU/h) 0.873 0 Heat utilization from boiler
8.203 (non-condensation) 7.385 (non-condensation) (mmBTU/h) 8.527
(condensation) 8.420 (condensation) Net heat utilization (mmBTU/h)
7.330 (non-condensation) 7.385 (non-condensation) 7.654
(condensation) 8.420 (condensation) Heat utilization efficiency (%)
66.5 (non-condensation) 67.0 (non-condensation) 69.5 (condensation)
76.4 (condensation) Flue gas mass flow rate (lb/h) 10,842 11,509
Adiabatic flame temperature (.degree. F.) 2,723 2,273 Thermal
equilibrium CO production 71 2.9 (ppm) Thermal equilibrium NOx
production 2,306 764 (ppm) Vapor content in flue gas (%) 8.9 17.3
CO2 in flue gas (%) 13.7 12.5 Assumptions: (1): the feed stock is
assumed to have properties similar to wood (2): the combustion air
is adjusted to have 8% O.sub.2 in flue gas.
The data in Tables 3 and 4 show the following.
(1) Without feed stock drying, the process generally provides
better overall heat utilization. When heat losses from dryer and
combustor are considered, the process without feed stock drying
will be even better, because a larger heat loss would be expected
when employing the dryer and combustor, since separate units will
be in use, that together will have a larger heat loss due to the
increased surface area as compared to just the combustor.
(2) With a higher water vapor presence in flue gas, the convective
heat transfer can be improved due to increased mass flow rate of
the convective gas (flue gas), which improves the heat
utilization.
(3) With a higher water vapor and lower CO.sub.2 concentration, the
radiation heat transfer between flue gas and heat transfer surface
may also be increased due to increased emissivity.
(4) Due to high water content in feed stock in case of without
drying, the flame temperature is low compared to the case w/
drying. As a result, the CO and NOx productions may be greatly
reduced if the wet feed stock is directly combusted.
(5) When a feed stock dryer is utilized, the overall capital and
operating costs are increased.
Thus, the effect of moisture on combustion processes must be
evaluated in the overall system approach. Drying a feed stock prior
to combustion does not necessarily result in savings or
improvements in overall usable energy, or increasing the overall
energy utilization efficiency. In addition, adding the extra step
of reducing the moisture content of fuel also adds extra capital
costs and operation and management costs. Burning a dry feed stock
increases the potentials of air pollutant productions including CO
and NOx. This is consistent with the common counter measure seen in
the industry whereby water is sprayed into the burner to lower the
flame temperature so as to reduce slagging (formation of ash) and
the negative effects of, among other things, the production of CO
and NOx.
Conversely, if the moisture content in the fuel is too high (e.g.
greater than about 50 wt %), the difficulty in maintaining stable
combustion significantly increases. Therefore, a moisture content
of about 10 wt % to about 40 wt % has been found to be optimal for
balancing efficiency and reactor operation.
Gasification Applications
Moisture can effect gasification in a variety of ways. For example,
if moisture is removed from the feed stock prior to being gasified,
gasification performance may, or may not, be improved, depending
upon which parameter of gasification is observed. In terms of
energy utilization efficiency, drying may not improve the overall
efficiency of gasification, unlike the effect of drying the feed
stock upon combustion applications as discussed above.
Depending upon the gasification application, oxidants such as air,
pure oxygen or steam can be used. In the case of oxygen large scale
coal gasification which operates at temperatures of typically
1500.degree. C., the oxygen consumption is high, which makes
slagging and melting of ash an operational challenge. The challenge
in this case is operating the gasification with a minimum amount of
gasifying feed stock required because this reduces the amount of
oxygen per unit product gas. This reduction is oxygen translates
into a larger savings during the gasification. However, with the
reduction in oxygen as the oxidant, more steam is then necessary.
Since more moisture is necessary, it can either be introduced into
the gasification unit or as in the present invention the necessary
moisture is present in the feed stock. This increase in moisture in
the feed stock, both reduces the amount of oxygen needed during
gasification as well as allows more control of the gasification
temperature, which increases carbon conversion, and thus improves
the overall gasification performance.
Furthermore, the thermodynamics and kinetics of the gasification
reaction are effected by the amount of moisture during the
gasification reaction. Two reactions that occur during the
gasification reaction are given below: C+1/2O2=CO (a)
C+H.sub.2O.dbd.CO+H.sub.2 (b)
Though the thermodynamics and kinetics dictate that most of the
gasification will be accomplished via reaction (a), the reaction
given in (b) allows every carbon that is gasified via steam yields
two molecules of synthesis gas per atom of carbon with steam, which
is less extensive in comparison with only one carbon in reaction
(a) via oxygen, which is much more expensive. To force reaction (b)
to predominate during gasification the presence of sufficient
moisture is important.
It is obvious that a process that produces a syngas containing a
relatively high methane content and therefore a high cold gas
efficiency will be useful in a power application. However, such a
syngas composition may not be the optimum choice for a different
syngas application in which syngas requires an optimum H.sub.2/CO
yield. By varying the moisture content in feed stock the syngas
production rate and composition can be enhanced in order to favor
or disfavor one particular application. The effect of moisture can
have on gasifier performance and syngas properties also varies
according to the characteristics of the feed stock. For example,
the chemically bonded moisture and carbon content are two
parameters that can influence of moisture on the feed stock during
gasification. For a high carbon content fuel, such as dry coal, in
which chemically bonded moisture is low, increasing the moisture
content improves syngas production rate by stimulating reaction (b)
above, and improves syngas heating value. In contrast, for feed
stock having high chemically bonded moisture, such as wood, further
increasing the moisture content results in a lower gasification
efficiency, although it increases the hydrogen production and thus
H.sub.2/CO ratio, by promoting the water-gas shift reaction
(reaction (b) above). At lower gasification temperatures the
moisture content may also increase methane production which results
in a syngas suitable for power generation applications. In the
presence of moisture at high gasification temperatures, methane
production will be reduced.
Thus, the appropriate moisture content in gasification feed stock,
like steam injection into gasifiers, is a useful and economic
gasification moderator, which can achieve at least one of the
following:
(a) Controlling the Gasifier Temperature:
FIG. 5 shows the predicted effect of moisture on gasification
temperature, carbon conversion and H.sub.2+CO production rate for a
typical coal feed stock at a constant air equivalence (ER) ratio
(ER=0.34). Higher moisture containing feed stock, when gasified,
can lower the gasification temperature which allows higher ash
content feed stocks to be gasified. Operation of the gasifier at
lower temperatures is preferred for such engineered fuel feed
stocks due to their propensity for slagging or ash fusion. Presence
of moisture in feed stock also increases the conversion of carbon,
making low temperature operation of the gasification possible while
still being capable of reducing the potential risk of ash slagging,
fusion.
(b) Alternating the Syngas Production:
As steam injection is often needed to control the gasification
temperature, and condition the syngas compositions, particularly
methane production and H.sub.2/CO ratio to suit for particular
syngas applications (for power generation or chemical synthesis).
FIG. 6 shows the predicted variation of syngas compositions with
feed stocks of different moisture contents for a typical wood feed
stock at 800.degree. C.
(c) Increasing Carbon Conversion:
Due to promotion of the water-gas shift reaction
(CO+H.sub.2O.dbd.CO.sub.2+H.sub.2), higher or complete carbon
conversion can be achieved at reduced gasification temperatures.
This not only allows the lower temperature operation, but also
improves the CO+H.sub.2 production rate, and gasification
efficiency. However, when the moisture is too high, the CO+H.sub.2
production rate and cold gas efficiency may decline because of
increased combustion (to provide heat necessary for attaining the
same gasification temperature). FIG. 7 shows the predicted effect
of fuel moisture content on carbon conversion, cold gas efficiency
and CO+H.sub.2 production rate for a typical coal feed stock at
850.degree. C. FIG. 8 shows the predicted effect of fuel moisture
content on carbon conversion, cold gas efficiency and CO+H.sub.2
production rate for pure carbon at 1000.degree. C.
(d) As an Oxidant:
FIG. 9 shows the predicted total and external water supply required
to produce a syngas of H.sub.2/CO=2.0 at 850.degree. C. for a
typical wood feed stock. Moisture in feed stock can replace the
external steam supply in case steam is used as oxidant, which is
often the case when external heat is available, and/or saving
oxygen is desired. By replacing air or oxygen as the oxidant, by
water from feed stock, a high BTU syngas can be produced due to
reduced dilution of nitrogen, and increased water-gas reaction (b).
In addition to increasing the H.sub.2/CO ratio, the H.sub.2+CO
production rate and cold gas efficiency will be slightly increased
with increasing moisture when operating at a constant gasification
temperature and air-equivalence ratio (FIG. 8). FIG. 10 shows the
predicted CO+H.sub.2 production rate, cold gas efficiency and
H.sub.2/CO ratio at 850.degree. C. and an ER=0.30 for a typical
wood feed stock.
By judiciously selecting for components of MSW according to, for
example, parameters discussed above, and negatively or positively
selecting the components from the MSW waste stream, followed by
blending of the components, and optionally any other additives
deemed necessary, in the correct proportions, engineered fuel feed
stocks can be engineered for a specified use. For example, Table 5
lists some common components found in MSW, along with their C, H,
O, N, S, ash, and HHV content, as well as the ER required for
complete combustion. The components can be sorted into any
different number of classes, according to, for example, their
carbon content. For example, MSW can be sorted into two, three,
four, five or even more classes. In one embodiment, Table 5a lists
four separate classes: class #1 has a carbon content of about 45%,
class #2 has a carbon content of about 55%, class #3 has a carbon
content of about 60%, and class #4 has a carbon content of about
75%.
TABLE-US-00005 TABLE 5 HHV Air at Sorted (BTU/ ER = 1 Waste C H O N
S A lb) (lb/lb) Wood 49.5 6 42.7 0.2 0.1 1.5 8,573 5.9 Food waste
48 6.4 37.6 2.6 0.4 5 8,714 6.1 Paper 43.5 6 44 0.3 0.2 6 7,595 5.2
Cardboard 44 5.9 44.6 0.3 0.2 5 7,585 5.2 Yard waste 47.8 6 38 3.4
0.3 4.5 8,387 5.9 Textiles 55 6.6 31.2 4.6 0.15 2.5 10,093 7.2
Plastics 60 7.2 22.8 0 0 10 11,795 8.4 Leather 60 8 11.6 10 0.4 10
12,340 9.1 Rubber 78 10 0 2 0 10 17,154 12.4 ##STR00001##
TABLE-US-00006 TABLE 5a Air at HHV ER = 1 Waste Class C H O N S A
(BTU/lb) (lb/lb) Class #1 45.0 6.1 41.4 1.4 0.2 4.4 8171 5.6 Class
#2 55.0 6.6 31.2 4.6 0.2 2.5 10,093 7.2 Class #3 60.0 7. 617.2 5.0
0.2 10.0 12,067 8.7 Class #4 75.0 10.0 0.0 2.0 0.0 10.0 17,154
12.4
In order to engineer a fuel possessing certain specified
parameters, equation 1 can be used to select from, and assign the
amounts from, the four classes listed in Table 5a.
.function..function..times..function..times..function..times..function..t-
imes..function..times..function..times..times. ##EQU00004##
where
.times..times.<<.times.<<.times..times..times..times.
##EQU00005##
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times. ##EQU00005.2##
For example, an engineered fuel feed stock made from MSW can be
designed to have the same chemical composition as natural
woodchips. Natural woodchips have the chemical composition listed
in Table 6. The precise amounts of the different classes of sorted
MSW listed in Table 5 needed for engineering a synthetic fuel of
the same chemical composition as natural woodchips were determined
according to eq. 1 to be 88.1% from class #1 and 11.9% from class
#2. No components from classes #3 and #4 were required for this
particular synthetic engineered fuel feed stock.
TABLE-US-00007 TABLE 6 Air at HHV ER = 1 Molecular Chemical C H O N
S A (BTU/lb) (lb/lb) Weight Formula Engineered 47.6 6.1 40.2 1.7
0.2 4.2 8,400 5.8 24.2 CH.sub.1.54O.sub.0.66N- .sub.0.031 Fuel
Simulating Woodchips Wood 49.5 6.0 42.7 0.2 0.1 1.5 8,573 5.9 23.7
CH.sub.1.45O.sub.0.63N.sub.0- .033 chips
The ultimate and proximate chemical analysis of woodchips and FS#4
are tabulated in Table 7.
TABLE-US-00008 TABLE 7 FS#4 Wood 82% Newsprints, 18% Wood pellets
Plastics AR MF AR MF Moisture 6.51 3.64 Ash 0.54 0.58 9.62 9.98
Volatile 82.03 87.74 77.26 80.18 Fixed Carbon 10.92 11.68 9.48 9.84
S 0 0.01 0.08 0.01 H 5.39 5.77 5.45 5.66 C 45.58 48.75 41.81 43.39
N 0.01 0.01 0.07 0.07 O 41.98 44.90 39.33 40.82 Cl H/C 0.12 0.12
0.13 0.13 O/C 0.92 0.92 0.94 0.94 HHV (BTU/lb) 7,936 8,489 7,296
7,572 HHV (BTU/lb), 8,225 7,520 Calculated Density (lb/cu. ft) 41.8
33.7
Gasification tests were performed at a laboratory scale stratified
downdraft gasifier. The gasifier has an inside diameter of 4 inches
and a height of 24 inches above a perforated grate. There are four
Type-K thermocouples installed along the gasifier, 1'', 7'', 19''
above the grate and 4'' below the grate. The real-time temperatures
are recorded by a data logger thermometer (OMEGA, HH309A). A syngas
sampling train, consisting of two water scrubbers, and a vacuum
pump is used for taking syngas samples, which is analyzed by a
HP5890A gas chromotograph to obtain volumetric fractions of H2, N2,
CO, CO2 and CH4. A dry gas test meter is installed in the air
entrance to measure the air intake rate. The tests with two wood
and simulated wood were conduced with air as oxidant at similar
operating conditions. The results are listed in Table 8.
TABLE-US-00009 TABLE 8 Simulated Wood Parameter Wood (FS#4) H2 20.3
19.8 N2 44.8 46.4 CO 24.1 24.7 CH4 2.0 1.2 CO2 8.7 8.0 H2/CO 0.84
0.80 BTU/scf 167.4 159.2
As can be observed in Table 8, the amounts of H.sub.2, N.sub.2, CO,
CH.sub.4, CO.sub.2 produced from the gasification of woodchips are
very similar to those produced from the gasification of feed stock
#4. In addition, the ratio of H.sub.2/CO and the BTU/scf is within
about 5%. This engineered fuel feed stock demonstrates that by
using the methods described herein, feed stocks can be engineered
that approximate a natural fuel such as wood.
Fuels of Similar Energy Content do not Necessarily Demonstrate
Similar Gasification or Combustion Profiles
However is does not follow that two fuels possessing the same
energy content (for example HHV or BTU/lb) will combust or gasify
with the same reactivity or produce the same thermal conversion
profile. For example, two feed stocks were prepared containing
approximately 14,000 BTU/lb. Feed stock #2 (FS#2) has an energy
content of 13,991 BTU/lb and feed stock #7 (FS#7) has an energy
content of 14,405 BTU/lb, a difference of about 3%. The chemical
molecular characteristics of the two feed stocks are listed in
Table 9. The moisture content, carbon content, hydrogen content,
oxygen content, and ratios of H/C and O/C are very different
compared to each other.
TABLE-US-00010 TABLE 9 FS#2 FS#7 80% Rubber, 36% Magazines, 20%
Paper + 13% 64% Plastics water AR MF AR MF Moisture 0.94 13.1 Ash
6.53 6.59 3.84 4.42 Volatile 92.48 93.36 61.94 71.28 Fixed Carbon
0.05 0.05 21.12 24.30 S 0.05 0.01 1.28 0.01 H 9.51 9.60 5.87 6.75 C
68.85 69.50 75.12 86.44 N 0.01 0.01 0.03 0.03 O 14.12 14.25 0.77
0.89 Cl 0.076 0.09 C/H 7.2 7.2 12.8 12.8 C/O 4.9 4.9 97.6 97.6 HHV
(BTU/lb) 13,991 14,124 14,405 16,577 HHV (BTU/lb), 15,064 16,574
Calculated Density (lb/cu. ft)
The feed stocks were gasified using the following procedure.
Gasification tests were performed at a laboratory scale stratified
downdraft gasifier. The gasifier has an inside diameter of 4 inches
and a height of 24 inches above a perforated grate. There are four
Type-K thermocouples installed along the gasifier, 1'', 7'', 19''
above the grate and 4'' below the grate. The real-time temperatures
are recorded by a data logger thermometer (OMEGA, HH309A). A syngas
sampling train, consisting of two water scrubbers, and a vacuum
pump is used for taking syngas samples, which is analyzed by a
HP5890A gas chromatograph to obtain volumetric fractions of
H.sub.2, N.sub.2, CO, CO.sub.2 and CH.sub.4. A dry gas test meter
is installed in the air entrance to measure the air intake rate.
The tests with two wood and simulated wood were conduced with air
as oxidant at similar operating conditions. The results are listed
in the following table. It can be seen that syngas composition,
H.sub.2/CO ratio and syngas HHV are fairly close between the two
engineered fuel feed stocks. The results of the gasification of
feed stocks FS#2 and FS#7 are listed in Table 10.
TABLE-US-00011 TABLE 10 Parameter FS#2 FS#7 Difference % H.sub.2 %
21.9 28.6 30.4 N.sub.2 % 45.6 45.2 0.8 CO % 18.9 15.6 17.2 CH.sub.4
% 6.4 2.7 57.3 CO.sub.2 % 7.3 7.9 8.6 H.sub.2/CO 1.16 1.83 57.4
Syngas HHV (BTU/scf) 200.21 173.8 13.2 CO + H.sub.2 % 40.8 44.2
8.4
From the data in Table 10, it can be seen that although the two
fuels have very similar energy content (a difference of only about
3%), the difference in syngas composition is very different. There
is a greater than 30% difference in H.sub.2 vol. % and CH.sub.4
vol. % and an over 50% difference in the ratio of H.sub.2/CO
between the two feed stocks, which means that the synthesis gases
from these two fuels could not be used for the production of
similar Fischer-Tropsch fuels. There is a 13% difference in the
energy content of the synthesis gas and a 17% difference in the
amount of CO produced between the two feed stocks. This experiment
demonstrates that consideration of only the BTU/lb value of feed
stocks does not give a true indication of what type of syngas
profile the feed stock will have.
Combustion
The same calculation was performed on theoretical feed stocks
except the condition were under combustion rather than
gasification. All feed stocks were assumed to have the same HHV of
10,000 BTU/lb, and then changes to the combinations of carbon
content, hydrogen content, oxygen content, ash content and moisture
content were introduced. The results are tabulated in Table 11.
TABLE-US-00012 TABLE 11 #1 #2 #3 #4 #5 BTU Value/lb 10,000 10,000
10,000 10,000 10,000 Moisture 5 5 5 5 5 Ash 5 5 5 5 5 S 0.1 0.1 0.1
0.1 0.1 H 13.3 10.1 6.9 3.7 0.5 C 30 40 50 60 70 N 0.1 0.1 0.1 0.1
0.1 O 46.6 39.7 32.9 26.1 19.3 C/H 2.3 4.0 7.3 16.4 147.3 C/O 0.6
1.0 1.5 2.3 3.6 Stoich. Air (scf/lb) 78.8 83.2 87.7 92.2 96.7
Combustion Products Excess Air Ratio 28.5% 29.5% 30.0% 31.0% 32.0%
O2 (scf/lb) 4.7 5.2 5.5 6.0 6.5 N2 (scf/lb) 80.0 85.2 90.1 95.4
100.8 CO2 (scf/lb) 9.5 12.7 15.8 19.0 22.1 H2O (scf/lb) 26.2 20.1
14.1 8.0 2.0 SO2 (scf/lb) 0.012 0.012 0.012 0.012 0.012 Total
(scf/lb) 120.4 123.1 125.5 128.4 131.4 Flue Gas (dry %) O2 (dry
vol. %) 5.0 5.0 5.0 5.0 5.0 N2 (dry vol. %) 84.9 82.7 80.8 79.2
77.9 CO2 (dry vol. %) 10.1 12.3 14.2 15.8 17.1 SO2 (dry, ppmv) 126
115 106 99 92
As can be seen in Table 11, theoretical feed stocks #1 to #5 all
have the same HHV of 10,000 BTU/lb, but the carbon content varies
from 30% to 70% (H and O will also vary accordingly). From the
numbers listed the stoichiometric air requirement for complete
combustion varies from 78.8 to 96.7 scf per lb of feed stock. Due
to this difference, combustion products will vary, and noticeably
the excess air ratio must be adjusted in actual combustion
operation if the operator is monitoring stack O.sub.2. In the above
calculations, excess air has to be adjusted from 28.5% for feed
stock #1 to 32% for feed stock #5 if the target O.sub.2 in stack is
at 5%.
TABLE-US-00013 TABLE 12 #3 #8 #9 #10 BTU Value/lb Moisture 5 10 15
20 Ash 5 5 5 5 S 0.1 0.1 0.1 0.1 H 6.9 5.6 4.4 3.2 C 50 50 50 50 N
0.1 0.1 0.1 0.1 O 32.9 29.2 25.4 21.6 C/H 7.3 8.9 11.3 15.6 C/O 1.5
1.7 2.0 2.3 Stoich. Air (scf/lb) 87.7 84.3 81.0 77.6 Combustion
Products Excess Air Ratio 30.0% 30.5% 31.0% 31.0% O2 (scf/lb) 5.5
5.4 5.3 5.0 N2 (scf/lb) 90.1 86.9 83.8 80.3 CO2 (scf/lb) 15.8 15.8
15.8 15.8 H2O (scf/lb) 14.1 12.8 11.6 10.3 SO2 (scf/lb) 0.012 0.012
0.012 0.012 Total (scf/lb) 125.5 121.0 116.4 111.4 Flue Gas (dry %)
O2 (dry vol. %) 5.0 5.0 5.0 5.0 N2 (dry vol. %) 80.8 80.4 79.9 79.4
CO2 (dry vol. %) 14.2 14.6 15.1 15.6 SO2 (dry, ppmv) 106 110 113
117
In Table 12 the theoretical feed stocks each have an energy value
of 10,000 BTU/lb but the moisture content was varied from between
5% to 20%. The stoichiometric air requirement for complete
combustion varies from 87.7 for #3 (5% moisture) to 77.6 for #10
(20% moisture) scf per lb of feed stock. Thus, for combustion
operation, consideration of only the BTU content of a feed stock is
insufficient to know what the combustion profile will be. Feed
stocks possessing the same BTU value but different chemical
molecular characteristics will exhibit different combustion
behavior and require different combustion controls. It is also
anticipated that the combustor temperature will also vary even with
feed stocks containing the same BTU value yet having different
chemical molecular characteristics.
Design of High BTU Fuels
To design the maximum BTU containing fuel while minimizing the risk
of slagging, a limit on the amount of ash present must be taken
into account. For biomass fuels, it has been reported that fuels
comprising less than about 5% ash appear not to slag as much as
fuels containing more than about 5% ash (see Reed, T. B., and A.
Das, Handbook of Biomass Downdraft Gasifier Engine Systems. Golden:
SERI, 1988). Ashes can cause a variety of problems particularly in
up or downdraft gasifiers. Slagging or clinker formation in the
reactor, caused by melting and agglomeration of ashes, at the best
will greatly add to the amount of labor required to operate the
gasifier. If no special measures are taken, slagging can lead to
excessive tar formation and/or complete blocking of the
reactor.
Whether or not slagging occurs depends on the ash content of the
fuel, the melting characteristics of the ash, and the temperature
pattern in the gasifier. Local high temperatures in voids in the
fuel bed in the oxidation zone, caused by bridging in the bed and
maldistribution of gaseous and solids flows, may cause slagging
even using fuels with a high ash melting temperature. In general,
no slagging is observed with fuels having ash contents below 5-6
percent. Severe slagging can be expected for fuels having ash
contents of 12 percent and above. For fuels with ash contents
between 6 and 12 percent, the slagging behavior depends to a large
extent on the ash melting temperature, which is influenced by the
presence of trace elements giving rise to the formation of low
melting point eutectic mixtures. Equation 2 below gives the
relationship between the energy content of the fuel (HHV) and the
amount of ash contained in the engineered fuel feed stock.
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times. ##EQU00006##
.times..times.< ##EQU00007## (to minimize risk of slagging)
.times..times. ##EQU00008## (less than a predetermined value)
.times..times..times..times..times..times..times..times..times..times..ti-
mes. ##EQU00009##
By use of the above equations an engineered fuel feed stock with a
HHV of about 10,000 BTU/lb can be designed whereby the ash is held
to a minimum amount, for example, less than about 5% ash, or less
than about 4% ash. The components of MSW used to engineer the fuels
of about 10,000 BTU/lb were selected from the four classes of MSW
components derived from MSW listed in Table 5. Table 13 lists the
amounts of the components of MSW used for engineering these fuels
and their corresponding carbon, hydrogen, sulfur, and ash contents
as well as the HHV value for the engineered fuel.
TABLE-US-00014 TABLE 13 C H O N S Ash HHV (BTU/lb) Ash content <
4% 56.0 6.8 28.4 4.6 0.2 4.0 10,493 (80% Class #2, 20% Class #3)
Ash content < 5% 56.7 6.9 26.5 4.7 0.2 5.0 10,756 (67% Class #2,
33% Class #3)
Design of Engineered Fuel Feed Stock based on Target Syngas
Composition for Downstream Fischer-Tropsch Chemistry
In some embodiments, during production of the densified form of the
engineered fuel feed stock, it is determined that the chemical
molecular characteristic of the densified form is lower than that
required for a particular gasifier, the amount of other materials
that enhance the gasification process may be increased during the
process thereby bringing the chemical molecular characteristics of
the densified form of the engineered fuel feed stock within the
desired fuel specification. In other embodiments, other materials
that enhance the gasification process may be added before or during
the compression to adjust the chemical molecular characteristics of
the resulting densified form of the engineered fuel feed stock. In
some embodiments the other material added to the feed stock is a
FOG. Table 16 lists the heat content of certain FOGs and their
carbon and hydrogen contents.
TABLE-US-00015 TABLE 16 Type of FOG BTU/lb Carbon Content Hydrogen
Content Tallow 16,920 76.6% 11.9% Chicken Fat 16,873 75.3% 11.4%
Yellow Grease 16,899 76.4% 11.6% Choice White Grease 16,893 76.5%
11.5% Waste Motor Oil 16,900 Not available Not available
Another type of material that can be added to the feed stock is
sludge. Table 17 gives the carbon and hydrogen content of
sludge.
TABLE-US-00016 TABLE 17 Elemental Analysis Primary Secondary Mixed
Digested Carbon 60.0 53.0 57.0 67.0 Hydrogen 7.5 7.0 7.0 5.0 Oxygen
28.0 30.5 30.0 25.0 Nitrogen 3.0 9.0 5.0 2.2 Sulfur 1.5 0.5 1.0 0.8
Total 100 100 100 100
The best-known technology for producing hydrocarbons from synthesis
gas is the Fischer-Tropsch synthesis. This technology was first
demonstrated in Germany in 1902 by Sabatier and Senderens when they
hydrogenated carbon monoxide (CO) to methane, using a nickel
catalyst. In 1926 Fischer and Tropsch were awarded a patent for the
discovery of a catalytic technique to convert synthesis gas to
liquid hydrocarbons similar to petroleum.
The basic reactions in the Fischer-Tropsch synthesis are:
Paraffins: (2n+1)H.sub.2+nCO.fwdarw.C.sub.nH.sub.2n+2+nH.sub.2O
Olefins: 2nH2+nCO.fwdarw.C.sub.nH.sub.2n+nH.sub.2O
Alcohols:
2nH.sub.2+nCO.fwdarw.C.sub.nH.sub.2n+1OH+(n-1)H.sub.2O
Other reactions may also occur during the Fischer-Tropsch
synthesis, depending on the catalyst employed and the conditions
used:
Water-gas shift: CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2
Boudouard disproportionation: 2CO.fwdarw.C(s)+CO.sub.2
Surface carbonaceous deposition:
.times..times..times..times..times..times. ##EQU00010##
Catalyst oxidation-reduction: yH2O+xM.fwdarw.M.sub.xO.sub.y+yH2
yCO2+xM.fwdarw.M.sub.xO.sub.y+yCO
Bulk carbide formation: yC+xM.fwdarw.M.sub.xC.sub.y
where M represents a catalytic metal atom.
The production of hydrocarbons using traditional Fischer-Tropsch
catalysts is governed by chain growth or polymerization kinetics.
Equation 3 describes the production of hydrocarbons, commonly
referred to as the Anderson-Schulz-Flory equation.
.function..times..times..alpha..alpha..differential..times.
##EQU00011##
where W.sub.n=weight fraction of products with carbon number n, and
.alpha.=chain growth probability, i.e., the probability that a
carbon chain on the catalyst surface will grow by adding another
carbon atom rather than terminating. In general, a is dependent on
concentrations or partial pressures of CO and H2, temperature,
pressure, and catalyst composition but independent of chain length.
As a increases, the average carbon number of the product also
increases. When .alpha. equals 0, only methane is formed. As a
approaches 1, the product becomes predominantly wax.
FIG. 11 provides a graphical representation of eq. 2 showing the
weight fraction of various products as a function of the chain
growth parameter .alpha.. FIG. 11 shows that there is a particular
.alpha. that will maximize the yield of a desired product, such as
gasoline or diesel fuel. The weight fraction of material between
carbon numbers m and n, inclusive, is given by equation 4:
W.sub.mn=m.alpha..sup.m-1-(m-1).alpha..sup.m-(n+1).alpha..sup.n+n.alpha..-
sup.n+1 (eq. 4)
The .alpha. to maximize the yield of the carbon number range from m
to n is given by equation 5.
.alpha..times..times. ##EQU00012##
Additional gasoline and diesel fuel can be produced through further
refining, such as hydrocracking or catalytic cracking of the wax
product.
For each of the targeted products derived from syngas the
corresponding appropriate H.sub.2/CO ratio is needed. One way to
produce such H.sub.2/CO ratio is to control the amount of C, H, and
O in the feed stock used to produce the syngas. For example, FIG.
12 shows the predicted C/H and C/O ratios needed in the feed stock
in order to produce a syngas of the requisite H.sub.2/CO ratio.
TABLE-US-00017 TABLE 14 H.sub.2/CO Product Basic Chemical Reaction
Ratio FT Liquid 2n H.sub.2 + n CO .fwdarw. C.sub.nH.sub.2n + n
H.sub.2O; 2:0-2.1 fuels (2n + 1)H.sub.2 + n CO .fwdarw.
C.sub.nH.sub.2n+1 + n H.sub.2O Methanol 2 H.sub.2 +
CO.dbd.CH.sub.3OH; CO.sub.2 + 3 H.sub.2 .fwdarw. 2.0 CH.sub.3OH +
H.sub.2O Ethanol 2 CO + 4 H.sub.2 .fwdarw. C.sub.2H.sub.5OH +
H.sub.2O 2.0 Higher n CO + 2n H.sub.2 .fwdarw. C.sub.nH.sub.2n+1OH
+ (n - 1) H.sub.2O 2.0 alcohols Dimethyl 2 CO + 4 H.sub.2 .fwdarw.
CH.sub.3OCH.sub.3 + H.sub.2O 2.0 ether Acetic Acid 2 CO + 2 H.sub.2
.fwdarw. CH.sub.3COOH 1.0 Ethylene 2 CO + 4 H.sub.2 .fwdarw.
C.sub.2H.sub.4 + 2H.sub.2O 2.0 Ethylene 2 CO + 3 H.sub.2 .fwdarw.
C.sub.2H.sub.6O.sub.2 1.5 Glycol Ac.sub.2O 4 CO + 4 H.sub.2
.fwdarw. (CH.sub.3CO).sub.2O + H.sub.2O 1.0 Ethyl Acetate 4 CO + 6
H.sub.2 .fwdarw. CH.sub.3COOC.sub.2H.sub.5 + 2 H.sub.2O 1.50 Vinyl
Acetate 4 CO + 5 H.sub.2 .fwdarw. CH.sub.3COOCH.dbd.CH.sub.2 + 2
H.sub.2O 1.25
By first selecting the H.sub.2/CO ratio desired in the product
syngas, the proper ratio of H/C and O/C in the composition of the
engineered feed stock can be determined, along with the proper
amount of moisture and ash content. Once these ratios have been
determined then the proper MSW components can be selected and
combined together to form feed stocks that upon gasification will
yield a syngas with the desired H.sub.2/CO ratio.
Physical Properties that Affect Efficient Gasification or
Combustion of Fuel Particles
Up and downdraft gasifiers are limited in the range of fuel size
acceptable in the feed stock. Fine grained and/or fluffy feed stock
may cause flow problems in the bunker section of the gasifier as
well as an inadmissible pressure drop over the reduction zone and a
high proportion of dust in the gas. Large pressure drops will lead
to reduction of the gas load of downdraft equipment, resulting in
low temperatures and tar production. Excessively large sizes of
particles or pieces give rise to reduced reactivity of the fuel,
resulting in startup problems and poor gas quality, and to
transport problems through the equipment. A large range in size
distribution of the feed stock will generally aggravate the above
phenomena. Too large particle sizes can cause gas channeling
problems, especially in updraft gasifiers. Acceptable fuel sizes
fox gasification systems depend to a certain extent on the design
of the units.
Particle size distribution in fuel influences aspects of combustor
and gasifier operations including the rate at which fuel reacts
with oxygen and other gases. Smaller particles of fuel tend to be
consumed faster than bigger ones. Particle size is based on
area-volume average (d.sub.pv) (eq. 6). The distribution of
particle sizes in a population of particles is given by d.sub.pv
(eq. 7):
.times..pi..times..times..times..times. ##EQU00013##
The shape of the engineered fuel feed stock particles and the
densified form of the engineered fuel feed stock also strongly
influence the rates of gas-solid reactions and momentum transfers
between the particles and the gas stream that carries them. One
parameter used to describe the shape of a particle is sphericity,
which affects the fluidity of the particles during the
gasification/combustion process. Fluidity is important in avoiding
channeling and bridging by the particles in the gasifier, thereby
reducing the efficiency of the conversion process. Sphericity can
be defined by the following formula:
.phi..times..times..times..times..times..times..times..times..times..time-
s..times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times..times..times..times..times..times..times.
##EQU00014##
Particle size, d.sub.pv, and sphericity, .phi..sub.p together in
the relationship .phi..sub.pd.sub.pv, influence hydrodynamic
characteristics of particles while in a combustor or gasifier.
These hydrodynamic characteristics include among others pressure
drop, minimum fluidization velocity, terminal velocity and momentum
transfer. By way of example, particles of coal, limestone, and
sand, present with sphericity that ranges from 0.6 to 0.9.
Woodchips particles, for example, present with a sphericity of
about 0.2.
The rates of gas-solids reactions depend on the available surface
area of the particle. Therefore, for particles of similar volumes,
the particle with the higher surface area will be consumed faster
and more efficiently and therefore effect the gasification process.
Equations 8 and 9 describe the volume of a sphere and cylinder,
respectively.
.times..alpha..times..times..pi..times..times..pi..times..times..times..p-
i..times..times..times..times. ##EQU00015##
Table 15 below lists different cylinders and a sphere that all have
the same volume (0.524 in.sup.3), yet possessing different surface
areas (in.sup.2) and specific surface areas
(in.sup.2/in.sup.3).
TABLE-US-00018 TABLE 15 Specific Characteristic Average Surface
Volume surface area dimensions diameter area (in.sup.2) (in.sup.3)
(in.sup.2/(in.sup.3) Sphericity Sphere .phi.1'' .phi.1'' 3.142
0.524 6.0 1 Cylindrical .phi.0.5'' .times. 2.667'' .phi.1'' 4.518
4.518 8.75 0.686 Cylindrical 0.87'' .times. 0.88'' .phi.1'' 3.596
3.596 6.87 0.874 Cylindrical .phi.1.0'' .times. 0.667'' .phi.1''
3.665 3.665 7.0 0.857 Cylindrical .phi.1.5'' .times. 0.296''
.phi.1'' 4.931 4.931 9.471 0.637
For shapes with the same volume such as cylinders and spheres,
spheres have the lowest specific surface area. As the sphericity of
a cylinder approaches 1 it behaves more like a sphere in the
gasification/combustion process. However, the surface area for the
corresponding volume is not maximized in the shape of a sphere
which means the conversion process will not be optimally efficient.
There is a minimum specific surface area and highest sphericity for
a cylindrical shape depending on its diameter and length. This
shape when determined for the engineered fuel is optimal for the
conversion process for which the fuel is used. FIG. 13 shows that
when the cylindrical diameter is plotted against the sphericity and
the cylindrical length and specific area, the optimal size of the
pellet can be determined.
For a given equivalent diameter, (FIG. 13), there is a minimum in
specific surface area corresponding to a maximum sphericity when
the cylindrical diameter almost equals its length. Away from this
point, the sphericity decreases but the specific surface area
increases which means that while the fluidity is declining, the
rates of gas-solid reactions becomes favored. The optimal pellet
dimensions have a maximum possible specific surface area while
maintaining a sphericity value high enough to ensure excellent
fluidity. This parameter minimizes or even prevents bridging and
channeling of pellets inside the gasifiers, which decreases the
efficiency of the conversion process.
As described above, the engineered feed stock should provide
maximum surface area for the same volume in order to favor
gas-solid reactions which is determined by maximization of .alpha.p
in eq. 10.
.times..times..alpha..times..times..pi..times..times..pi..times..times..t-
imes..pi..times..times..times..times. ##EQU00016##
The maximization of up for a particular feed stock provides better
hydrodynamic performance during the conversion process and cost
effectiveness in preparation (size reduction and pelletizing) of
the engineered fuel as compared to other natural fuels.
For further optimization of combustion or gasification performance,
the size and shape, and in some embodiments, the sphericity, of the
engineered fuel feed stock can be determined. For example, to
engineer a fuel having a densified form that will produce similar
results as compared with, for example, natural woodchips in
gasification and combustion processes, the sphericity of natural
woodchips provides a natural starting point. Natural woodchips have
a sphericity (.phi..sub.p) of about 0.2. An engineered fuel
particle was designed with a sphericity of 0.25, a slightly better
sphericity than natural woodchips yet containing the same HHV.
Equation 11 describes the size of the engineered fuel particle and
Table 18 lists the possible dimensions for such an engineered
particle:
.PHI..pi..function..times..pi..gtoreq..times..times..times..times..times.-
.times..PHI..times..gtoreq..times..times..times..times..times.
##EQU00017##
TABLE-US-00019 TABLE 18 Overall particle size (in) 1.0 1.5 2.0
Diameter (in) 0.83 1.35 1.91 Length (in) 1.67 1.93 2.21 Specific
Surface Area (ft.sup.2/ft.sup.3) 72 48 36
From the values shown in Table 18, the smallest particle actually
has the greatest specific surface area (72 ft.sup.2/ft.sup.3 versus
48 ft.sup.2/ft.sup.3 and 36 ft.sup.2/ft.sup.3, respectively).
The rate of gasification of the fuel pellets can be positively
effected by a number of elements which act as catalysts, such as
small quantities of potassium, sodium or zinc.
Bulk density is defined as the weight per unit volume of loosely
tipped fuel. Fuels with high bulk density are advantageous because
they represent a high energy-for-volume value. Low bulk density
fuels sometimes give rise to insufficient flow under gravity,
resulting in low gas heating values and ultimately in burning of
the char in the reduction zone. Average bulk densities of solid
fuels such as wood, coal and peat ranges from about 10 lb/ft.sup.3
to about 30 lb/ft.sup.3. If bulk densities for some components used
for the pellets of the invention are too low, the over all bulk
density can be improved through pelletization. The bulk density
varies significantly with moisture content and particle size of the
fuel.
Exemplary ranges for specifications of a waste feed for a
gasification system can include, but are not limited to: a diameter
of between about 0.25 inches to about 1.5 inches; a length of
between about 0.5 inch to about 6 inches; a surface to volume ratio
of between about 20:1 to about 3:1; a bulk density of about 10
lb/ft.sup.3 to about 75 lb/ft.sup.3; a porosity of between about
0.2 and about 0.6; an aspect ratio of between about 1 to about 10;
a thermal conductivity of between about 0.023 BTU/(fthr.degree. F.)
and about 0.578 BTU/(fthr.degree. F.); a specific heat capacity of
between about 4.78.times.10.sup.-5 to 4.78.times.10.sup.-4
BTU/(lb.degree. F.); a thermal diffusivity of between about
1.08.times.10.sup.-5 ft.sup.2/s to 2.16.times.10.sup.-5 ft.sup.2/s;
a HHV of between about 3,000 BTU/lb to about 15,000 BTU/lb; a
moisture content of about 10% to about 30%; a volatile matter
content of between about 40% to about 80%; a carbon content of
between about 30% to about 80%; a hydrogen content of between about
3% to about 10%, a sulfur content of less than 2%; a chlorine
content of less than 1%; and an ash content of less than about
10%.
From the results show in FIG. 14, MSW feed stock can be classified
according to its carbon content and thus its potential for
producing the amount of CO and H.sub.2 in the resulting syngas upon
thermal conversion. Table 19 shows one classification of types of
fuels based on carbon content: low heat fuels (less than 45 wt %
carbon); moderate heat fuels (45-60 wt % carbon); and high heat
fuels (>60 wt % carbon).
TABLE-US-00020 TABLE 19 Low Heat Fuels Moderate Heat Fuels High
Heat Fuels Carbon content <45 wt % 45-60 wt % >60 wt %
H.sub.2 + CO Product <10 scf/lbs 10-20 scf/lbs >20 scf/lbs
Air Equivalence ratio >0.35 0.1-0.35 <0.1 Syngas HHV (dry
basis) <120 BTU/scf 120-200 BTU/scf >200 BTU/scf Gasifier
temperature <850.degree. C. 800-900.degree. C. >900.degree.
C. Performance Incomplete C Complete carbon Complete carbon
conversion, conversion, minimal conversion, no formation of CH4
formation of CH4 formation of CH.sub.4 and tars and tars, low risk
and tars, high risk of slagging of slagging Applications Syngas for
combustion Syngas for all Syngas for all applications (engines),
power, liquid fuel power, liquid fuel co-gasification w/other and
chemicals and chemicals fuels including moderate applications
applications and high heat fuels as well as LFG
The low heat fuels can be characterized as producing syngas
containing CO and H.sub.2 at less than about 10 scf/lbs and an HHV
of less than about 120 BTU/scf. Because the gasifier requires an
air equivalence ratio of more than 0.35 because of the low amount
of carbon, the gasifier temperature will not rise above about
850.degree. C. causing incomplete conversion of carbon and the
formation of methane and tars. These fuels can be used for
production of syngas for all purposes, co-gasification with other
fuels including moderate and high heat fuels, as well as LFG.
The moderate heat fuels can be characterized as producing syngas
containing CO and H.sub.2 at about 10 to about 20 scf/lbs and an
HHV of about 120 to about 200 BTU/scf. Because the gasifier
requires an air equivalence ratio of about 0.1 to about 0.35 with a
carbon content of about 45 wt % to about 60 wt %, the gasifier
maintains a temperature of about 850.degree. C. to about
900.degree. C. causing complete conversion of carbon, minimal
formation of methane and tars, and low risk of slagging. These
fuels can be used for production of syngas for all applications,
liquid fuels, and chemicals applications.
The high heat fuels can be characterized as producing syngas
containing CO and H.sub.2 at greater than about 20 scf/lbs and an
HHV of greater than 200 BTU/scf. Because the gasifier requires an
air equivalence ratio of only less than about 0.1 with a carbon
content of greater than about 60 wt %, the gasifier's temperature
is generally greater than about 900.degree. C. causing complete
conversion of carbon, no formation of methane and tars, but a high
risk of slagging. These fuels can be used for production of syngas
for all applications, liquid fuels, and chemicals applications.
Therefore depending on the end use of the syngas to be produced,
engineered fuel feed stocks of different carbon content can be
selected and fuels can be engineered and synthesized for a
particular end use. Such selection allows the fine tuning of the
engineered fuels produced from differing heterogeneous feed stocks
such as MSW, FOGS, sludges, etc. The engineered fuels can be used
for producing syngas containing the desired CO and H.sub.2
content.
The MSW can be processed by any method that allows for
identification and separation of the component parts according to
material type, such as by plastics, fibers, textiles, paper in all
its forms, cardboard, rubber, yard waste, food waste, and leather.
Methods of separation such as those disclosed in U.S. Pat. No.
7,431,156, US 2006/0254957, US 2008/0290006, US 2008/0237093, the
disclosures of which are hereby incorporated in their entirety, can
be used for separating the components of waste.
It is understood that modifications may be made to the methods of
separation disclosed above that allow for the recovery of the
individual components of MSW for use in engineering engineered fuel
feed stock as described herein.
In some embodiments, the component or components of the engineered
feed stock are mixed. In some of the embodiments, the mixed
components are reduced in size using known techniques such as
shredding, grinding, crumbling and the like. Methods for the
reduction in size of MSW components is well known and for example
are described in U.S. Pat. No. 5,888,256, the disclosure of which
is incorporated by reference in its entirety. In other embodiments,
the individual components are first reduced in size prior to mixing
with other components. In some embodiments, the mixed components of
the engineered fuel feed stock are densified using known
densification methods such as, for example, those described in U.S.
Pat. No. 5,916,826, the disclosure of which is incorporated by
reference in its entirety. In some embodiments, the densification
forms pellets by the use of a pelletizer, such as a Pasadena hand
press, capable of exerting up to 40,000 force-pounds.
In some embodiments, the FOGS component is added directly to the
mixing tank. In other embodiments, the FOGS component is added
after mixing just before the waste is placed into a pelletizing
die.
By use of a pelletizer under appropriate conditions, pellets are
produced having a range of dimensions. The pellets should have a
diameter of at least about 0.25 inch, and especially in the range
of about 0.25 inches to about 1.5 inches. The pellets should have a
length of at least about 0.5 inch, and especially in the range of
about 0.5 inches to about 6 inches.
By selection of the appropriate die to be used with the pelletizer,
the pellets become scored on the surface of the encapsulation. This
scoring may act as an identifying mark. The scoring can also affect
the devolatization process such that the scored pellets volatize at
a more efficient rate than the unscored pellets.
In some embodiments, the engineered fuel feed stock described
herein is biologically, chemically and toxicologically inert. The
term biologically inert, chemically inert, and toxicologically
inert means that the engineered fuel feed stock described herein
does not exceed the EPA's limits for acceptable limits on
biological, chemical and toxicological agents contained within the
engineered fuel feed stock. The terms also include the meaning that
the engineered fuel feed stock does not release toxic products
after production or upon prolonged storage. The engineered fuel
feed stock does not contain, for example pathogens or live
organisms, nor contain the conditions that would promote the growth
of organisms after production or upon prolonged storage. For
example, the engineered fuel feed stock in any form described
herein can be designed so as to have a moisture content sufficient
so as not to promote growth of organisms. The engineered fuel feed
stock can be designed to be anti-absorbent, meaning it will not
absorb water to any appreciable amount after production and upon
prolonged storage. The engineered fuel feed stock is also air
stable, meaning it will not decompose in the presence of air to
give off appreciable amounts of volatile organic compounds. The
engineered fuel feed stock described herein may be tested according
to known methods in order to determine whether they meet the limits
allowed for the definition of inert. For example, 40 CFR Parts 239
through 259 promulgated under Title 40--Protection of the
Environment, contains all of the EPA's regulations governing the
regulations for solid waste. The EPA publication SW-846, entitled
Test Methods for Evaluating Solid Waste, Physical/Chemical Methods,
is OSW's official compendium of analytical and sampling methods
that have been evaluated and approved for use in complying with 40
CFR Parts 239 through 259, in relation to solid waste, which is
incorporated by reference herein in its entirety.
EXAMPLES
Reference will now be made to specific examples some of which
illustrate the invention. It is to be understood that the examples
are provided to illustrate preferred embodiments and that no
limitation to the scope of the invention is intended thereby.
General Synthetic Procedures
After components for the engineered feed stock were selected they
were shredded in a low speed shredder and then mixed mechanically.
Afterwards the mixture was densified using a pelletizer. If the
moisture content needed to be increased, water was added during the
mixing step. A small sample of the feed stock was taken and dried
in an temperature controlled and vented oven to confirm the
moisture content. The mixed engineered feed stock was then
subjected to gasification as described above.
Feed Stock Wood (Control)
TABLE-US-00021 Wood Wood pellets AR MF Moisture 6.51 Ash 0.54 0.58
Volatile 82.03 87.74 Fixed Carbon 10.92 11.68 S 0 0.01 H 5.39 5.77
C 45.58 48.75 N 0.01 0.01 O 41.98 44.90 Cl C/H 8.5 8.5 C/O 1.1 1.1
HHV (BTU/lb) 7,936 8,489 HHV (BTU/lb), Calculated 8,225 Density
(lb/cu. ft) 41.8
Feed Stock #1
TABLE-US-00022 Feed stock #1 (FS#1) 82% Newsprints, 18% Plastics AR
MF Moisture 3.25 Ash 4.51 4.66 Volatile 86.43 89.33 Fixed Carbon
5.81 6.01 S 0 0.01 H 7.57 7.82 C 51.88 53.62 N 0.06 0.06 O 32.65
33.75 Cl C/H 6.9 6.9 C/O 1.6 1.6 HHV (BTU/lb) 9,552 9,873 HHV
(BTU/lb), Calculated 10,696 Density (lb/cu. ft) 20.3
Feed Stock #1 Gasifier Output
TABLE-US-00023 Hydrogen, vol % 14.9 Nitrogen, vol % 51.6 Carbon
Monoxide, vol % 18.9 Methane, vol % 2.3 Carbon Dioxide, vol % 12.3
Hydrogen/Carbon Monoxide 0.79 BTU/scf 134.79 Carbon Monoxide +
Hydrogen 33.8
Feed Stock #2
TABLE-US-00024 FS#2 36% Magazines, 64% Plastics AR MF Moisture 0.94
Ash 6.53 6.59 Volatile 92.48 93.36 Fixed Carbon 0.05 0.05 S 0.05
0.05 H 9.51 9.60 C 68.85 69.50 N 0.01 0.01 O 14.12 14.25 Cl C/H 7.2
7.2 C/O 4.9 4.9 HHV (BTU/lb) 13,991 14,124 HHV (BTU/lb), Calculated
15,064 Density (lb/cu. ft)
Feed Stock #2 Gasifier Output
TABLE-US-00025 Hydrogen, vol % 21.9 Nitrogen, vol % 45.6 Carbon
Monoxide, vol % 18.9 Methane, vol % 6.4 Carbon Dioxide, vol % 7.3
Hydrogen/Carbon Monoxide 1.16 BTU/scf 200.21 Carbon Monoxide +
Hydrogen 40.8
Feed Stock #3
TABLE-US-00026 FS#3 24.5% Other Papers, 75.5% Textiles AR MF
Moisture 1.57 Ash 7.57 7.69 Volatile 75.12 76.32 Fixed Carbon 15.74
15.99 S 0.37 0.38 H 5.85 5.94 C 48.12 48.89 N 8.38 8.51 O 28.14
28.59 Cl 3.44 3.49 C/H 8.2 8.2 C/O 1.7 1.7 HHV (BTU/lb) 9,629 9,783
HHV (BTU/lb), Calculated 8,705 Density (lb/cu. ft) 21.9
Feed Stock #3 Gasifier Output
TABLE-US-00027 Hydrogen, vol % 6.5 Nitrogen, vol % 64.6 Carbon
Monoxide, vol % 19.3 Methane, vol % 0.3 Carbon Dioxide, vol % 9.3
Hydrogen/Carbon Monoxide 0.3 BTU/scf 88.6 Carbon Monoxide +
Hydrogen 25.7
Feed Stock #4
TABLE-US-00028 FS#4 91.8% Newsprint, 2.2% Plastics, 6.0% Yard
wastes AR MF Moisture 3.64 Ash 9.62 9.98 Volatile 77.26 80.18 Fixed
Carbon 9.48 9.84 S 0.08 0.08 H 5.45 5.66 C 41.81 43.39 N 0.07 0.07
O 39.33 40.82 Cl C/H 7.7 7.7 C/O 1.1 1.1 HHV (BTU/lb) 7,296 7,572
HHV (BTU/lb), Calculated 7,520 Density (lb/cu. ft) 33.7
Feed Stock #4 Gasifier Output
TABLE-US-00029 Hydrogen, vol % 19.8 Nitrogen, vol % 46.4 Carbon
Monoxide, vol % 24.7 Methane, vol % 1.2 Carbon Dioxide, vol % 8.0
Hydrogen/Carbon Monoxide 0.80 BTU/scf 159.2 Carbon Monoxide +
Hydrogen 44.5
Feed Stock #5
TABLE-US-00030 FS#5 68% paper; 32% Rubber AR MF Moisture 1.35 Ash
9.11 9.23 Volatile 77.18 78.24 Fixed Carbon 12.36 12.53 S 0.23 0.01
H 5.84 5.92 C 45.92 46.55 N 0.01 0.01 O 37.55 38.06 Cl 0.219 0.22
C/H 7.9 7.9 C/O 1.2 1.2 HHV (BTU/lb) 9,250 9,377 HHV (BTU/lb),
Calculated 8,288 Density (lb/cu. ft)
Feed Stock #5 Gasifier Output
TABLE-US-00031 Hydrogen, vol % 14.9 Nitrogen, vol % 51.6 Carbon
Monoxide, vol % 17.0 Methane, vol % 3.4 Carbon Dioxide, vol % 13.1
Hydrogen/Carbon Monoxide 0.88 BTU/scf 140.56 Carbon Monoxide +
Hydrogen 31.8
Feed Stock #6
TABLE-US-00032 FS#6 100% Rubber AR MF Moisture 0.06 Ash 6.12 6.12
Volatile 68.46 68.50 Fixed Carbon 25.36 25.38 S 1.92 0.01 H 6.78
6.78 C 81.73 81.78 N 0.18 0.18 O 3.21 3.21 Cl C/H 12.1 12.1 C/O
25.5 25.5 HHV (BTU/lb) 15,780 15,789 HHV (BTU/lb), Calculated
15,768 Density (lb/cu. ft) 28.6
Feed Stock #6 Gasifier Output
TABLE-US-00033 Hydrogen, vol % 8.65 Nitrogen, vol % 68.2 Carbon
Monoxide, vol % 14.5 Methane, vol % 0.71 Carbon Dioxide, vol % 6.9
Hydrogen/Carbon Monoxide 0.60 BTU/scf 83.7 Carbon Monoxide +
Hydrogen 23.2
Feed Stock #7
TABLE-US-00034 FS#7 80% Rubber, 20% Paper + 13% water AR MF
Moisture 13.1 Ash 3.84 4.42 Volatile 61.94 71.28 Fixed Carbon 21.12
24.30 S 1.28 0.01 H 5.87 6.75 C 75.12 86.44 N 0.03 0.03 O 0.77 0.89
Cl 0.076 0.09 C/H 12.8 12.8 C/O 97.6 97.6 HHV (BTU/lb) 14,405
16,577 HHV (BTU/lb), Calculated 16,574 Density (lb/cu. ft)
Feed Stock #7 Gasifier Output
TABLE-US-00035 Hydrogen, vol % 28.6 Nitrogen, vol % 45.2 Carbon
Monoxide, vol % 15.6 Methane, vol % 2.7 Carbon Dioxide, vol % 7.9
Hydrogen/Carbon Monoxide 1.83 BTU/scf 173.8 Carbon Monoxide +
Hydrogen 44.2
Example 1
TABLE-US-00036 Test Method AS AIR DRY ASTM.sup.1 # Parameter
RECEIVED DRIED BASIS D 3302, Total Moisture, 21.04 -- -- 5142 % wt
D 5142 Residual Moisture, -- 7.04 -- % wt D 5142 Ash, % wt 12.91
15.20 16.35 D 5142 Volatile, % wt 58.81 69.24 74.49 Calculation
Fixed Carbon, % wt 7.24 8.52 9.16 Total 100.00 100.00 100.00 D 4239
Sulfur % 0.18 0.21 0.23 D 5865 HHV Btu/lb (Gross) 10890 12821 13792
D 3176 Hydrogen, % wt 4.24 4.99 5.37 D 3176 Carbon, % wt 33.84
39.84 42.86 D 3176 Nitrogen, % wt 0.24 0.29 0.31 Calculation %
Oxygen by 27.55 32.42 34.88 difference .sup.1American Society for
Testing and Materials
Example 2
TABLE-US-00037 Test Method AS AIR DRY ASTM.sup.1 # Parameter
RECEIVED DRIED BASIS D 3302, Total Moisture, 13.26 -- -- 5142 % wt
D 5142 Residual Moisture, -- 6.09 -- % wt D 5142 Ash, % wt 14.39
15.58 16.59 D 5142 Volatile, % wt 63.33 68.57 73.02 Calculation
Fixed Carbon, % wt 9.02 9.76 10.40 Total 100.00 100.00 100.00 D
4239 Sulfur % 0.20 0.22 0.23 D 5865 HHV Btu/lb (Gross) 11165 12088
12872 D 3176 Hydrogen, % wt 5.55 6.01 6.40 D 3176 Carbon, % wt
41.68 45.12 48.05 D 3176 Nitrogen, % wt 0.21 0.23 0.24 Calculation
% Oxygen by 24.71 26.75 28.49 difference .sup.1American Society for
Testing and Materials
Example 3
TABLE-US-00038 Test Method AS AIR DRY ASTM.sup.1 # Parameter
RECEIVED DRIED BASIS D 3302, Total Moisture, % wt 15.06 -- -- 5142
D 5142 Residual Moisture, % wt -- 4.16 -- D 5142 Ash, % wt 11.67
13.17 13.74 D 5142 Volatile, % wt 64.60 72.89 76.05 Calculation
Fixed Carbon, % wt 8.67 9.78 10.21 Total 100.00 100.00 100.00 D
4239 Sulfur % 0.09 0.11 0.11 D 5865 HHV Btu/lb (Gross) 6188 6982
7285 D 3176 Hydrogen, % wt 4.93 5.56 5.80 D 3176 Carbon, % wt 34.90
39.38 41.09 D 3176 Nitrogen, % wt 0.07 0.08 0.08 Calculation %
Oxygen by difference 33.28 37.55 39.18 D4208 Chlorine, % wt 0.75
0.84 0.88 .sup.1American Society for Testing and Materials
Example 4
TABLE-US-00039 Test Method AS AIR DRY ASTM.sup.1 # Parameter
RECEIVED DRIED BASIS D 3302, Total Moisture, % wt 14.99 -- -- 5142
D 5142 Residual Moisture, % wt -- 1.88 -- D 5142 Ash, % wt 16.48
19.03 19.39 D 5142 Volatile, % wt 62.84 72.53 73.92 Calculation
Fixed Carbon, % wt 5.69 6.56 6.70 Total 100.00 100.00 100.00 D 4239
Sulfur % 0.06 0.07 0.07 D 5865 HHV Btu/lb (Gross) 6782 7828 7978 D
3176 Hydrogen, % wt 4.48 5.17 5.27 D 3176 Carbon, % wt 31.94 36.96
37.57 D 3176 Nitrogen, % wt 0.08 0.09 0.09 Calculation % Oxygen by
difference 31.97 36.80 37.61 D 4208 Chlorine, % wt 1.17 1.35
1.38
Example 5
TABLE-US-00040 Test Method AS ASTM.sup.1 # Parameter RECEIVED DRY
BASIS Pellet Composition: 80% Fiber/20% plastic E 939 Total
Moisture, % wt 13.26 -- E 830 Ash, % wt 5.24 6.04 E 897 Volatile, %
wt 62.97 72.60 D 3172 Fixed Carbon, % wt 18.53 21.36 Total 100.00
100.00 D 4239 Sulfur % 0.15 0.17 E 711 HHV Btu/lb (Gross) 8806
10152 D 6373 Hydrogen, % wt 6.66 7.67 D 6373 Carbon, % wt 48.4 55.8
D 5373 Nitrogen, % wt 0.15 0.18 Calculation % Oxygen by difference
26.14 30.14 D 4208 Chlorine, % wt 0.06 0.07 .sup.1American Society
for Testing and Materials
Example 6
TABLE-US-00041 Test Method AS ASTM.sup.1 # Parameter RECEIVED DRY
BASIS Pellet Composition: Plastics #2, and #4-7 E 939 Total
Moisture, % wt 2.1 -- E 830 Ash, % wt 7.82 7.98 E 897 Volatile, %
wt 89.32 91.24 D 3172 Fixed Carbon, % wt 0.76 0.78 Total 100.00
100.00 D 4239 Sulfur % 0.17 0.17 E 711 HHV Btu/lb (Gross) 17,192
17,560 D 6373 Hydrogen, % wt 13.57 13.86 D 6373 Carbon, % wt 78.85
80.54 D 5373 Nitrogen, % wt 0.01 0.01 D 4208 Chlorine, % wt 0.33
0.34 .sup.1American Society for Testing and Materials
Example 7
TABLE-US-00042 Test Method AS ASTM.sup.1 # Parameter RECEIVED DRY
BASIS Pellet Composition: Paper E 939 Total Moisture, % wt 5.16 --
E 830 Ash, % wt 41.79 44.06 E 897 Volatile, % wt 48.27 50.90 D 3172
Fixed Carbon, % wt 4.78 5.04 Total 100.00 100.00 D 4239 Sulfur %
0.17 0.18 E 711 HHV Btu/lb (Gross) 5146 5426 D 6373 Hydrogen, % wt
3.65 3.85 D 6373 Carbon, % wt 30.55 32.21 D 5373 Nitrogen, % wt
0.43 0.45 Calculation % Oxygen by difference 18.25 19.25 D 4208
Chlorine, % wt 0.47 0.50 .sup.1American Society for Testing and
Materials
Example 8
TABLE-US-00043 Test Method AS ASTM.sup.1 # Parameter RECEIVED DRY
BASIS Pellet Composition: 10% Fiber/90% plastic E 939 Total
Moisture, % wt 2.53 -- E 830 Ash, % wt 12.64 12.97 E 897 Volatile,
% wt 83.50 85.67 D 3172 Fixed Carbon, % wt 1.33 1.36 D 4239 Sulfur
% 0.17 0.17 E 711 HHV Btu/lb (Gross) 15,482 15,885 D5373 Hydrogen,
% wt 12.16 12.48 D5373 Carbon, % wt 71.99 73.86 D5373 Nitrogen, %
wt 0.07 0.07 Calculation % Oxygen by difference 0.44 0.45 D4208
Chlorine, % wt 0.35 0.36 .sup.1American Society for Testing and
Materials
While particular embodiments described herein have been illustrated
and described, it would be obvious to those skilled in the art that
various other changes and modifications can be made without
departing from the spirit and scope of the disclosure. It is
therefore intended to cover in the appended claims all such changes
and modifications that are within the scope of this invention.
* * * * *